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Old 01-22-2019, 09:36 PM
Jinx Jinx is offline
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Rainbows: Why Not Just Three Colors?

This thought just hit me out of the blue today (no pun intended): If there are just three primary colors of light, then why isn't a rainbow simply comprised of just those three colors? Have our teachers been lying to us all these years? Could it be that a strategically placed spectrum could break down the remaining (non-prime) colors into JUST the prime colors? How do you all you Newtons out there in the "Arched" Dope FIGure this?

Last edited by Jinx; 01-22-2019 at 09:37 PM.
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Old 01-22-2019, 11:01 PM
Petrobey Mavromihalis Petrobey Mavromihalis is offline
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The 3 primary colours of light are a consequence of our vision rather than a feature of light itself, which simply varies in frequency 'smoothly' from what we call radiowaves to gamma rays. I think the seven identified colours of the rainbow are something to do with Newton's mystical beliefs in the number.
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Old 01-23-2019, 12:33 AM
Petrobey Mavromihalis Petrobey Mavromihalis is offline
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Further to my previous post have a look here to see a graph of our eyes sensitivity to different wavelengths of light. The three peaks correspond to the 3 primary colours of light, and incidentally make colour TVs / displays much easier.
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Old 01-23-2019, 12:52 AM
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Out of three primary colors comes three secondary colors so we have 6 basic colors. Reason we see millions of colors is of luminosity and transparency.

Look at our computer graphics. We use three colors, Yellow-Magenta-Cyan to produce over 16 million colors (256x256x256) that we can see.
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Old 01-23-2019, 01:30 AM
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Originally Posted by SigMan View Post
Out of three primary colors comes three secondary colors so we have 6 basic colors. Reason we see millions of colors is of luminosity and transparency.

Look at our computer graphics. We use three colors, Yellow-Magenta-Cyan to produce over 16 million colors (256x256x256) that we can see.
Primary colors are a cultural convention. Seeing millions of colors is a function of anatomy and neurology.

Our display technologies use RGB (red, green, blue) to synthesize colors additively. Cyan, magenta, and yellow are used with black (CMYK) in printing to synthesize colors subtractively.

https://cs.nyu.edu/courses/fall02/V2...lor_theory.htm

https://en.wikipedia.org/wiki/Primary_color
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Old 01-23-2019, 03:16 AM
Deflagration Deflagration is offline
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Here's a simplified example: Let's take the yellow light from the rainbow. We could take a singe wavelength of pure yellow light and shine it into our eye. Because the pure yellow activates both our green and red receptors at a certain percentage each we perceive the colour (correctly) as yellow.

Now let's shine a mix of red and green light, in the same ratios, into our eye. Again, because the receptors are stimulated in the same way, we perceive the exact same yellow. But it isn't.

The first is pure yellow. The second is a 'fake' yellow. To us they are identical. To a spectrometer it's a single peak compared to a completely different double peak.
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Old 01-23-2019, 03:27 AM
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Out of three primary colors comes three secondary colors so we have 6 basic colors. Reason we see millions of colors is of luminosity and transparency.
This is utterly wrong.

Light is a spectrum of electromagnetic radiation in specific wavelengths that happen to be visible to the human eye. The fact that we perceive certain colors more vibrantly is a quirk of how our eyes evolved a certain set of cone cells. There is no discrete point between one color and the next. The idea of there being only six discrete colors that mix together is just plain wrong. There are no limits to the number of colors in the world, but there are practical limits to what differences in wavelengths our eyes can detect.

The reason we talk about what my daughter calls the “M&M colors” is entirely arbitrary. Visit different cultures and you will find colors are defined differently. To directly answer OP, your teacher did in fact lie to you... In the sense that they often teach an over-simplified version to young children.

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Originally Posted by Sigman
Look at our computer graphics. We use three colors, Yellow-Magenta-Cyan to produce over 16 million colors (256x256x256) that we can see.
Also completely wrong.

The idea of blending colors out of three “primary” colors is useful when you are dealing with “subtractive” mediums like paint and crayons, and of course ink. Therefore, for practical and arbitrary reasons the printing industry arbitrarily decided that four colors of ink (Cyan, Magenta, Yellow, and Black) were “good enough.”

The fact that Cyan, Magenta, and Yellow are not objectively THE primary colors should be self-evident for two reasons:

(1) They are NOT the colors your TV uses. Your TV uses Red, Green, and Blue light because, again, the TV manufacturers decided it was “good enough.”

(2) Magenta is NOT a real color. Magenta is a combination of two specific wavelengths hitting your eye. Magenta does not exist on the visible spectrum. If you define a primary color as ‘a color we mix to make other colors’ then Magenta fails by even that definition.
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Old 01-23-2019, 04:15 AM
Aspidistra Aspidistra is offline
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I don't know about anyone else, but if I were to categorise the colours of the rainbow from scratch, without knowing the cultural convention, I'd probably come up with "Red Orange Yellow Green Blue Purple".

This "Indigo Violet" stuff is for the birds
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Old 01-23-2019, 05:13 AM
Deflagration Deflagration is offline
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Originally Posted by Aspidistra View Post
I don't know about anyone else, but if I were to categorise the colours of the rainbow from scratch, without knowing the cultural convention, I'd probably come up with "Red Orange Yellow Green Blue Purple".

This "Indigo Violet" stuff is for the birds
Absolutely. Except you can safely slip cyan between green and blue. And purple is actually nearer to "technically violet" as the naming on UV (Ultra Violet) shows.

And as stated above, you'll never get magenta in a rainbow. It's a constructed colour, always a mix and this never a single wavelength...

...Look at your rainbow. Red ain't next to Blue.
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Old 01-23-2019, 06:18 AM
Francis Vaughan Francis Vaughan is offline
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And as stated above, you'll never get magenta in a rainbow. It's a constructed colour, always a mix and this never a single wavelength...

...Look at your rainbow. Red ain't next to Blue.
Right to a very good first approximation. But there is a sting in the tale. We see violet, and that is past pure blue. We should not perceive a spectral colour past the peak of blue sensitivity if you use a simple RGB mixing model. The sting is that there is a tiny blip in the red sensitivity in the far blue, and our brain actually does get a small mix of red with blue when seeing spectrally pure violet.

Part of the reason is that our eyes don't have red green and blue sensors anyway. They have three sensor types that have very broad sensitivity, but with different slopes and break points across the spectrum. Subtract the signal of one from the others in different combinations and you can get the differences as signals in the three colour bands. However even this isn't done, they eye processes the three different sensors into a luminance and two difference signals, and they is what is pumped back into the brain. (I was really impressed with some work done a while ago where the neurons in the back of the retina had their structure analysed and the logic of the interconnections reverse engineered, and out popped the sum and difference signals. Previously the nature of the signalling had been painstakingly derived by working through the precise colour sensitivity the eye brain system exhibits, and fitting the model to the way we see both spectrally pure and mixed colours.)
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Old 01-23-2019, 06:24 AM
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A rainbow does not have seven stripes. It does not have six stripes.

It has an infinite number of stripes, gradually shifting from one hue to another.

How many categories we choose to assign, and where the dividing line is, between one category and another, is entirely arbitrary.

If we wanted, we could pick a band between yellow and green, and label it chartreuse. If we wanted, we could pick a band between yellow and chartreuse, and name it something else. We can choose whatever boundaries and labels suit our purposes at the moment.
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Old 01-23-2019, 06:37 AM
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The sting is that there is a tiny blip in the red sensitivity in the far blue, and our brain actually does get a small mix of red with blue when seeing spectrally pure violet.
I love this. Gap in my knowledge filled. Thank you.
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Old 01-23-2019, 07:22 AM
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There is also a large cultural aspect to the perception/description of color. The Greek poet and philosopher Xenophanes, for instance, describes the rainbow as follows:
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Originally Posted by Xenophanes
She whom men call `Iris' is in reality a cloud, purple, red, and green to the sight.

(He was writing to dispel the notion that the rainbow was a manifestation of the goddess Iris, considering all such things to be simply poorly understood natural phenomena.) So he did consider the rainbow to have three colors.

Last edited by Half Man Half Wit; 01-23-2019 at 07:22 AM.
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Old 01-23-2019, 08:16 AM
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How many categories we choose to assign, and where the dividing line is, between one category and another, is entirely arbitrary.

If we wanted, we could pick a band between yellow and green, and label it chartreuse. If we wanted, we could pick a band between yellow and chartreuse, and name it something else. We can choose whatever boundaries and labels suit our purposes at the moment.
We did that a couple centuries ago. Wiki on 'orange':
Quote:
Before the late 15th century, the colour orange existed in Europe, but without the name; it was simply called yellow-red. Portuguese merchants brought the first orange trees to Europe from Asia in the late 15th and early 16th century, along with the Sanskrit naranga, which gradually became part of several European languages: "naranja" in Spanish, "laranja" in Portuguese, and "orange" in English.
I, for one, am hard pressed to find the indigo between the blue and violet in a rainbow.
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Old 01-23-2019, 08:18 AM
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I don't know about anyone else, but if I were to categorise the colours of the rainbow from scratch, without knowing the cultural convention, I'd probably come up with "Red Orange Yellow Green Blue Purple".

This "Indigo Violet" stuff is for the birds
Absolutely correct. I wrote an article about Indigo, which forms a chapter in my book How the Ray Gun Got Its Zap!


There are almost infinitely many colors in a spectrum. We do, indeed, have tristimulus vision, meaning that we have three degrees of color sensitivity, but we can use those to visualize a vast array of colors. The thing is that many colors that have very different spectral composition look exactly the same to us. It's why we can get away with representing an entire spectrum using three colors in printing, or three different phosphors on a TV screen, and so forth.

People have disagreed about how many colors there are throughout history and cultures. Our present claim to their being seven colors comes, not from ancient history and mysticism (as is frequently claimed), but from Sir Isaac Newton.

When Newton started writing his treatise on Optics, he imagined that there were five colors -- Red, Yellow, Green, Blue, and Violet. Some passages in the book still retain this Five Color scheme. Other colors were just mixtures of these.

But he changed his mind, for some reason. I suspect it was his playing around with the interference phenomenon called "Newton's Rings' (although he was not the first to discover it). If you separate white sunlight using a prism, you get a single red-to-violet spectrum. But if you place a hemispherical piece of glass rounded side down on an absolutely flat piece you will see concentric rings of color, centered at the poit where the pieces of glass touch. And these rings follow the same order as the prism-sepoarated colors -- red, yellow, green, blue, violet (to use his 5-coloor scheme). But then they repeat -- RYGBV-RYGBV - RYGBV. It's very much like the way keys on a piano or harpsichord repeat themselves, the way musical notes rise from octave to octave.

There's a characteristic length associated with the colrs, as Newton found when he calculated the sizes of the gaps between the two piece of glass. And the distances corresponding to "red" are integral multiples of each other, as are the distances corresponding to each of the other colors. To another mind, this might be seen as evidenced of the wavelength theory of light. But Newton was committed to the corpuscular theory of light that had it made of particles.* He did, however, make the connection with the tonal scale, and concluded that there ought to be seven colors in a spectrum, corresponding to the seven notes in an octave (if you ignore the repeated "C" or "do") He compared the relative lengths associated with his colors and found that they agreed nicely with the lengths of strings needed to make those notes, with Red, Yellow, Gren, Blue, and Violet fitting very nicely. But there was a gap between Red and Yellow, and another between Blue and Violet. Orange was the obvious choice between Red and Yellow, and its length fit perfectly. But he needed a color between Blue and Violet. So he INVENTED "Indigo". The only reason it exists is to fill that gap in the color "scale". reportedly, newton used to try to persuade his friends that they could see an obvious color difference between Blue and Indigo.

I can't see it myself. Indigo is the plant they used to use to dye Blue Jeans. To me, it looks blue. Most people, I suspect, don't see the difference. The Universal Code for Resistors follows a rainbow order, but leaves out Indigo -- Brown Black Red Orange Yellow Green Blue Violet. The "Rainbow Flag"** you see most commonly either has only six colors (leaving out indigo) or else has a light blue or cyan in place of indigo.


By the way -- rainbows themselves don't always have seven, or even six obvious colors. The relative widths and appearance of the colors depends upon the sizes of the raindrops. If the raindrops are too small, diffraction from the small size fights against the separation refraction produces, making the colors blend together. In the most extreme cases of "mistbows", the bow is completely white, or may even have the orders reversed. M. Minnaert, in his classic book The Nature of Light and Color in the Open Air gives a handy chart that lets you determine the size of the raindrops from the observed widths and appearance of colors.




*Over a century later, when Thomas Young was championing the wave nature of light, he made the first measurement of the wavelengths using a fortuitous diffraction grating, and compared his values to Newton's.

** neither of these are the original "Diversity" Rainbow Flag, which actually has the colors in a slightly different order.
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Old 01-23-2019, 10:22 AM
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I’ve never understood the difference between violet and indigo. I know what those words are supposed to mean, but when I look at colors it’s all just “purple” as far as I’m concerned.

I also spent time in Korea and I learned they define the colors differently. Korean’s definitions of blue and green are slightly different from Americans.
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Old 01-23-2019, 10:37 AM
pulykamell pulykamell is online now
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We did that a couple centuries ago. Wiki on 'orange':I, for one, am hard pressed to find the indigo between the blue and violet in a rainbow.
I've always wondered if the "blue" Newton used was supposed to be more of a sky blue/cyan, and the indigo more of what we think of as regular Crayola blue. That would make a lot more sense to me, as when I look at a rainbow, there's (to me) a clear cyan-sky-blue as green transitions into deep blue, but not an obvious delineation between blue and violet, such that would necessitate naming another color (in this case, indigo) in between them.
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Old 01-23-2019, 10:53 AM
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You'll also sometimes (again, due to diffraction effects) see extra (or "supernumary") bands below the violet. To my eye, they stand out most prominently as alternating bands of green and purple.

And even without diffractive effects, the purely refractive effects will also result in each band having some thickness, as will the nonzero angular size of the Sun. That is to say, if you were to look at a large-drop (i.e., negligible diffraction) rainbow with an extremely high resolution telescope, so you're only looking at a tiny width of the rainbow, and fed that through a spectroscope, you'd still see some spread of wavelengths, just with the peak in different places.
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Old 01-23-2019, 11:14 AM
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You'll also sometimes (again, due to diffraction effects) see extra (or "supernumary") bands below the violet. To my eye, they stand out most prominently as alternating bands of green and purple.

And even without diffractive effects, the purely refractive effects will also result in each band having some thickness, as will the nonzero angular size of the Sun. That is to say, if you were to look at a large-drop (i.e., negligible diffraction) rainbow with an extremely high resolution telescope, so you're only looking at a tiny width of the rainbow, and fed that through a spectroscope, you'd still see some spread of wavelengths, just with the peak in different places.
Supernumerary rainbows are further evidence of the wave nature of light, and the diffractive nature of the rainbow itself -- you can't explain them if you assume that rainbows are a purely refractive phenomenon, and Thomas Young, ever on the lookout for evidence of the wave nature of light, eagerly seized on them as powerful evidence for his case. His math wasn't quite up to handling it, though, and it remained for George Biddell airy, director of the Greenwich Observatory in the early 19th century, to derive the Rainbow Integral and finally put the diffractive rainbow on a solid mathematical footing.



You only see the supernumerary rainbow if a.) the drops are all significantly larger than the wavelength of light; and b.) if the raindrops are all pretty nearly the same size. That's why they're comparatively rare. I've seen them in nature, though. as for why they're alternative pinkish-purple and aqua-green 9rather than repeating the spectrum, as with Newton's Rings0, it's because they're the result of Multiple Order white Light Interference. the overlapping out-of-synch orders produce basically pink and green light. You see the same effect in oil films and soap bubbles. I have an upcoming article on this (Entitled "Preppy Optics") in Optics and Photonics News.
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Old 01-23-2019, 11:57 AM
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I’ve never understood the difference between violet and indigo. I know what those words are supposed to mean, but when I look at colors it’s all just “purple” as far as I’m concerned.

I also spent time in Korea and I learned they define the colors differently. Korean’s definitions of blue and green are slightly different from Americans.
Indigo is a particular dye. Purple is a different particular dye. IMO they look quite different. That is without regard to names (and colour names differ greatly from language to language as you point out); of course violet is also named after a plant. So is fuchsia. Newton did not make up all the names himself.

Furthermore, in colour theory, there is an entire "line of purples" that are not in the rainbow spectrum; you get them by mixing red and violet or red and blue in various proportions.

As you noted, the names are all cultural/linguistic/artistic convention, but the (infinitely many) colors are quite real even when you call them all "shades of purple".
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Old 01-23-2019, 01:18 PM
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I wouldn't even say that the supernumary bands are particularly rare. When I was living in Montana, they seemed to show up in about half of the rainbows I saw (which was a fair number of them). Though this might ultimately just be a statement about the climate in Montana, that for whatever reason it's unusually apt to produce the conditions for supernumary bands (just as they also seemed unusually conducive to producing rainbows in the first place).
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Old 01-23-2019, 01:28 PM
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I wouldn't even say that the supernumary bands are particularly rare. When I was living in Montana, they seemed to show up in about half of the rainbows I saw (which was a fair number of them). Though this might ultimately just be a statement about the climate in Montana, that for whatever reason it's unusually apt to produce the conditions for supernumary bands (just as they also seemed unusually conducive to producing rainbows in the first place).
Utah, where I lived for a few years, was great for making rainbows -- the Wasatch mountains provided the conditions for clouds to dump rain, especially after having picked it up from the Great Salt Lake. If the sun was getting close to sunset at the time, the angle would be perfect for a rainbow. And with the mountains behind the bow, it'd be particularly visible. (And if the sun was very close to sunset, you'd get an orange-and-red Rainbow Sunset, since there was little green or blue present to b scattered.) and I do think that I saw more supernumeraries there than elsewhere. But it definitely wasn't even close to half the rainbows I saw.
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Old 01-23-2019, 01:34 PM
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Great info on the supernumary bands! I've seen them before and have wondered why there were sometimes extra bands in some rainbows (although apparently I didn't wonder enough to actually research it.)
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Old 01-23-2019, 01:35 PM
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I've always wondered if the "blue" Newton used was supposed to be more of a sky blue/cyan, and the indigo more of what we think of as regular Crayola blue. That would make a lot more sense to me, as when I look at a rainbow, there's (to me) a clear cyan-sky-blue as green transitions into deep blue, but not an obvious delineation between blue and violet, such that would necessitate naming another color (in this case, indigo) in between them.
From Wiki:

Later scientists conclude that Newton named the colors differently from current usage.[20][21] According to Gary Waldman, "A careful reading of Newton's work indicates that the color he called indigo, we would normally call blue; his blue is then what we would name blue-green, cyan or light blue."[22] If this is true, Newton's seven spectral colors would have been:

Red:  Orange:  Yellow:  Green:  Blue:  Indigo:  Violet:
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Old 01-23-2019, 02:30 PM
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From Wiki:

Later scientists conclude that Newton named the colors differently from current usage.[20][21] According to Gary Waldman, "A careful reading of Newton's work indicates that the color he called indigo, we would normally call blue; his blue is then what we would name blue-green, cyan or light blue."[22] If this is true, Newton's seven spectral colors would have been:

Red:  Orange:  Yellow:  Green:  Blue:  Indigo:  Violet:
There's no "if" about it. On those pages where he doesn't write about five colors (representing his older, pre-octave thinking), Newton in his Optics lists these seven colors, in this order.
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Old 01-23-2019, 02:43 PM
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And it's not too hard to reconstruct what each color was he was referring to, since he gives their characteristic lengths.
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Old 01-23-2019, 02:54 PM
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Ah, so his "blue" is indeed our cyan/sky blue, and "indigo" is our "blue." That makes a lot more sense to me if I were forced to divide the rainbow into seven colors.
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Old 01-23-2019, 02:55 PM
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There's no "if" about it. On those pages where he doesn't write about five colors (representing his older, pre-octave thinking), Newton in his Optics lists these seven colors, in this order.

Right-- Roy G. Biv.
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Old 01-23-2019, 03:03 PM
pulykamell pulykamell is online now
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There's no "if" about it. On those pages where he doesn't write about five colors (representing his older, pre-octave thinking), Newton in his Optics lists these seven colors, in this order.
But nobody is disputing the names of the colors. I'm curious as to what names the colors refererred to in modern English usage. It seems to me that ROY G. BIV is really what today would be ROY G. CBV or something like that.

Here's where the Wiki cite comes from with a graphic representing the colors today. "Blue" is a sky blue and "Indigo" is a deep blue. Kind of reminds me of the distinction in Russian between sky blue and deep blue, where they have individual words for the concept, rather than relying on an adjective to modify a base color name ("blue.")

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Old 01-23-2019, 03:17 PM
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Pythagoras named the colors: white, black, red, and yellow

Aristotle added blue, green, and purple

Newton did not subscribe to the earlier Emission theory and as earlier writers like Ptolemy had written about refraction white and black were dropped as colors.

Orange wasn't a named distinct color until orange trees arrived in Europe after the 15th century.

As color perception is a human trait and not a physical trait "roy g biv" is merely a social construct. There are some claims that Newtons seven colors could relate to Pythagoras' theory of music but I can't find any reliable historical documents to support this claim.

If someone has hard evidence that purple vs. indigo was based on anything more than cultural differences it would be appreciated.

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Old 01-23-2019, 03:21 PM
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The reason we talk about what my daughter calls the “M&M colors” is entirely arbitrary. Visit different cultures and you will find colors are defined differently. To directly answer OP, your teacher did in fact lie to you... In the sense that they often teach an over-simplified version to young children.
In Japan, they did not differentiate the color green until recently.

https://en.wikipedia.org/wiki/Ao_(color)

Green was considered a shade of blue and in many ways still is in Japanese language (for example a green traffic light is given the same name as their name for blue). Even the concept of green as a shade of blue didn’t come about until the Heian period (roughly 800-1200 CE) and calling them distinct colors only began after World War II with the American occupation.

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Old 01-23-2019, 03:26 PM
pulykamell pulykamell is online now
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(for example a green traffic light is given the same name as their name for blue).
I could actually see that. Depending on the traffic light and the type of lights being used, I find that what we call a "green" traffic like is closer to aqua blue. But it does vary a bit. And "yellow" is, to me, often closer to orange than it is yellow. (Calling it "amber" is actually most accurate to me, if choosing between "yellow," "amber," and "orange." And many places do call it "amber.")

Last edited by pulykamell; 01-23-2019 at 03:27 PM.
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Old 01-23-2019, 03:46 PM
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If someone has hard evidence that purple vs. indigo was based on anything more than cultural differences it would be appreciated.
Purple is Murex and indigo is Indigofera tinctoria. At least, that is what they are based on.

Azure versus cerulean versus cyan versus blue versus Japanese versus Russian colors, I'll let someone else fill in the details.
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Old 01-23-2019, 04:05 PM
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In Japan, they did not differentiate the color green until recently.
If one word was used for green and blue, why not translate it (at least before the 2nd word arose) as green?

Some linguists have observed the following:
All languages have at least 2 colors - white and black
Languages with 3+ colors have red.
Languages with 4+ have green or yellow
Languages with 5+ have green and yellow
Languages with 6+ have blue
Languages with 7+ have brown
Languages with 11+ have purple, pink, orange, gray.
I observe something like this in Thai. While they do have simple words for all eleven of these colors, in rural vernacular "lazy" approximations are often used: 'Red' for brown, and 'Green' for blue! (For example, a woman with dark brown hair is said to have 'red hair', less surprising than at first glance since most Thais' hair color is naturally jet black.)
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Old 01-23-2019, 04:32 PM
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If one word was used for green and blue, why not translate it (at least before the 2nd word arose) as green?
I suppose until the Heian period and “midori” you could have, but once that occurred you could see which word represented which color.

I guess it’s like, why do we call “pink” its own color when it’s just a light shade of red?
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Old 01-23-2019, 04:35 PM
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I suppose until the Heian period and “midori” you could have, but once that occurred you could see which word represented which color.

I guess it’s like, why do we call “pink” its own color when it’s just a light shade of red?
Actually, a lot of "pink" turns out not to be simply light red, but actually light purple -- it can't be represented by a single spectral line. You have to mix two spectral colors -- blue and red - in order to get the actual shade. Surprised me when I found out, because I, too, used to think that pink was simply "light red".
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Old 01-23-2019, 04:37 PM
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But nobody is disputing the names of the colors. I'm curious as to what names the colors refererred to in modern English usage. It seems to me that ROY G. BIV is really what today would be ROY G. CBV or something like that.
I don't think "cyan" is actually what Newton intended. The Cyan stripe on a seven-color rainbow flag looks horribly out-of-place.
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Old 01-23-2019, 04:53 PM
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I don't think "cyan" is actually what Newton intended. The Cyan stripe on a seven-color rainbow flag looks horribly out-of-place.
That is, or rather more of a sky blue, the color that is shown in the Wikipedia cite you mentioned, though.

Like in this version of the rainbow flag.

Maybe cyan is not quite the name for that light blue, but it's close enough. And I see it in other depictions of the rainbow.

Last edited by pulykamell; 01-23-2019 at 04:55 PM.
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Old 01-23-2019, 05:24 PM
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Note the "calico craze" which lead to the rise of indigo dyed fabrics from India during Newtons time wasn't just used for the "dark indigo" that Newton used in his "Opticks" but also for all shades of blue, and some greens and purples.

Apparently several countries implemented protections policies because the fad was impacting their local textile industries.

I am pretty sure that Newton used "indigo" due to that social fad vs using the word "purple".

I would bet that artists caused some drift from the names he was using.

Quote:
"appear tinged with this Series of Colours, violet, indigo, blue, green, yellow, orange, red, together with all their intermediate Degrees in a continual Succession perpetually varying. So that there appeared as many Degrees of Colours, as there were sorts of Rays differing in Refrangibility."
http://www.gutenberg.org/files/33504...-h/33504-h.htm

It appears that the Indian fabric fad is known to have increased the number of French words for different shades of blue so I would expect the same happened in England.
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Old 01-23-2019, 06:20 PM
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We can actually answer the question of what color Newton was naming "indigo" by using his own scheme of equating the musical notes with the characteristic lengths associated with the colors -- which we now know to be wavelengths. I ran the calculations, and found that Blue came out to be about 465 nm, indigo about 417, and Violet about 390. By comparison, Wikipedia and other sources give about 470 nm for blue, 450 for Indigo, and 420 for Violet.

You get slightly different values if, instead of the "Classical" values you use even tempering of your scale, but not that different -- 488 for Blue, 450 for Indigo, and 387 for Violet. You can look these up on a spectrum (although if you look at an on-line source, you won't really get proper color reproduction).

This is from a piece I wrote titled "The Well-Tempered Spectrometer", which hasn't yet been published.

If, instead of a simple octave, you go with a Chromatic Scale (which includes the "black keys" on the piano), you'll end up with a new color at 690 nm between Red and Orange, one aty 615 nm between Orange and Yellow, one at 516 between Green and Blue, one at 460 between Blue and Indigo, and one at 410 nm between Indigo and Violet.

Imagine that you're a modern-day Newton trying to buttonhole your friends into seeing these new colors, and come up with names for them.
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Old 01-23-2019, 07:54 PM
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We can actually answer the question of what color Newton was naming "indigo" by using his own scheme of equating the musical notes with the characteristic lengths associated with the colors -- which we now know to be wavelengths. I ran the calculations, and found that Blue came out to be about 465 nm, indigo about 417, and Violet about 390. By comparison, Wikipedia and other sources give about 470 nm for blue, 450 for Indigo, and 420 for Violet.

You get slightly different values if, instead of the "Classical" values you use even tempering of your scale, but not that different -- 488 for Blue, 450 for Indigo, and 387 for Violet. You can look these up on a spectrum (although if you look at an on-line source, you won't really get proper color reproduction).

This is from a piece I wrote titled "The Well-Tempered Spectrometer", which hasn't yet been published.

If, instead of a simple octave, you go with a Chromatic Scale (which includes the "black keys" on the piano), you'll end up with a new color at 690 nm between Red and Orange, one aty 615 nm between Orange and Yellow, one at 516 between Green and Blue, one at 460 between Blue and Indigo, and one at 410 nm between Indigo and Violet.

Imagine that you're a modern-day Newton trying to buttonhole your friends into seeing these new colors, and come up with names for them.
I get that Newton decided to mark seven (or 5+2?) colours, but what was his exact procedure? It seems a stretch to squeeze a full octave in there, for starters. And did he just name those seven colours and ask his friend to mark those off on a spectrum, or did he construct a tempered scale first, according to mathematical principles, and superimpose that onto the spectrum?

Looking at Newton's colour circle pictured here, it appears that the interval between Blue and Indigo is (approximately) equal to that between Indigo and Violet, but your equally-tempered ratios 488/450 and 450/387 do not match? Also, if we go for your chromatic version, wouldn't we need to split each of Red, Yellow, Green, Blue, and Violet into two, eliminating each of those colours in favor of two new ones?
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Old 01-23-2019, 10:56 PM
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Some linguists have observed the following:
All languages have at least 2 colors - white and black

Languages with 3+ colors have red.

Languages with 4+ have green or yellow

Languages with 5+ have green and yellow

Languages with 6+ have blue

Languages with 7+ have brown

Languages with 11+ have purple, pink, orange, gray.
Do you have a cite for this? I wonder how many languages there are around with only two words for colors, etc.
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Old 01-24-2019, 12:27 AM
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Do you have a cite for this? I wonder how many languages there are around with only two words for colors, etc.
Berlin & Kay's book on it was published back in 1969. The former Perfect Master known as Cecil did a column summarizing B&K's book. There's been a lot of research on this topic since, but I'm not aware of any good summary of it.
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Old 01-24-2019, 03:32 AM
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Do you have a cite for this? I wonder how many languages there are around with only two words for colors, etc.
The source I found yesterday, which cites the B&K book dtilque mentions, was "The Linguistic Significance of the Meanings of Basic Color Terms" (https://www.jstor.org/stable/412789) which
(a) may need you to register (for free) to read the 37-page article;
(b) needs $12 before presenting a version which allows copy-paste;
(c) was intended as a partial refutation of B&K's result;
(d) is more about vision physiology than language variations.

It does mention the Dugum Dani language of which Wikipedia writes:
Quote:
The Dani languages differentiate only two basic colours, mili for cool/dark shades such as blue, green, and black, and mola for warm/light colours such as red, yellow, and white. This trait makes it an interesting field of research for language psychologists, e.g. Eleanor Rosch, eager to know whether there is a link between way of thought and language.
In refutation of B&K, the jstor article mentions that 69% of Dani informants focused white-warm mola at Red.
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Old 01-24-2019, 04:06 AM
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Right to a very good first approximation. But there is a sting in the tale. We see violet, and that is past pure blue. We should not perceive a spectral colour past the peak of blue sensitivity if you use a simple RGB mixing model. The sting is that there is a tiny blip in the red sensitivity in the far blue, and our brain actually does get a small mix of red with blue when seeing spectrally pure violet.

Part of the reason is that our eyes don't have red green and blue sensors anyway. They have three sensor types that have very broad sensitivity, but with different slopes and break points across the spectrum. Subtract the signal of one from the others in different combinations and you can get the differences as signals in the three colour bands. However even this isn't done, they eye processes the three different sensors into a luminance and two difference signals, and they is what is pumped back into the brain. (I was really impressed with some work done a while ago where the neurons in the back of the retina had their structure analysed and the logic of the interconnections reverse engineered, and out popped the sum and difference signals. Previously the nature of the signalling had been painstakingly derived by working through the precise colour sensitivity the eye brain system exhibits, and fitting the model to the way we see both spectrally pure and mixed colours.)
And this is ultimately the answer to a question I asked in GQ long ago, of why we see red in violet. It's not in the cones (sensors), as I had originally supposed, but in the process of sending the visual signal to the brain. It's a quirk that allows us to identify colors beyond blue by mapping them partly into the red spectrum.

I presume the eye doesn't just send the raw signals to conserve bandwidth, as it would have to send signals from all the cones and the rods. Instead, some minimal processing occurs.
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Old 01-24-2019, 04:54 AM
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We can actually answer the question of what color Newton was naming "indigo" by using his own scheme of equating the musical notes with the characteristic lengths associated with the colors -- which we now know to be wavelengths. I ran the calculations, and found that Blue came out to be about 465 nm, indigo about 417, and Violet about 390. By comparison, Wikipedia and other sources give about 470 nm for blue, 450 for Indigo, and 420 for Violet.

You get slightly different values if, instead of the "Classical" values you use even tempering of your scale, but not that different -- 488 for Blue, 450 for Indigo, and 387 for Violet. You can look these up on a spectrum (although if you look at an on-line source, you won't really get proper color reproduction).
I did actually use an online source, for convenience. I agree with you that it isn't super accurate, but I think it can be useful, if what I say turns out to be true on most screens.

First set of numbers: Blue Indigo Violet
Second set of nums: Blue Indigo Violet

I then used GIMP to try and equalize the brightness, for a clearer comparison:
First set: Blue Indigo Violet
Second set: Blue Indigo Violet

Based on these results, the classical gives me what I would call blue, blue-violet, and red-violet. But the tempered gives me the cyan, blue, purple (slightly redder than violet).

I would expect that, to make it harmonious and fit the pure math, he'd use classical. Still, there are those color wheels that look more like he used even temperament. I could see him doing so to try and shoehorn in his theory.

I will finally leave you with this, since you seem to have some expertise, and can critique it: https://en.wikipedia.org/wiki/Indigo...spectral_color
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Old 01-24-2019, 07:26 AM
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I get that Newton decided to mark seven (or 5+2?) colours, but what was his exact procedure? It seems a stretch to squeeze a full octave in there, for starters.
I told you the procedure in my earlier post. Why do you think it's a "stretch" to "squeeze" an octave in there? You can divide any length by seven or eight.
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Old 01-24-2019, 07:32 AM
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Incidentally, I suspect that people continue to use "Indigo" and "Seven Colors" because of its long history (and social inertia), because there's more of a mystic association to "seven" than to "six", and so that Roy G. Biv will have a pronounceable last name. But they still use only six colors in a rainbow flag ( https://en.wikipedia.org/wiki/Rainbo...e:Gay_flag.svg ) and in the Resistor Code ( https://www.instructables.com/id/Res...or-Code-Guide/ )
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Old 01-24-2019, 07:43 AM
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The original Rainbow flag actually had 8 colors (pink and cyan/turquoise) were the additional two colors.
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Old 01-24-2019, 07:51 AM
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I would expect that, to make it harmonious and fit the pure math, he'd use classical. Still, there are those color wheels that look more like he used even temperament. I could see him doing so to try and shoehorn in his theory.
If you look at the wikipedia article posted on indigo above, there is
chart from Newton
that does show that each color band was not exactly the same size.

For me, when I look at a spectrum, there just seems to be a blindingly obvious stripe of light blue that seems like it should get a name.

Last edited by pulykamell; 01-24-2019 at 07:52 AM.
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