# Why is there colour? **URL:** \ **Category:** Factual Questions\ **Created:** [May 29, 2007, 1:43am UTC](https://boards.straightdope.com/t/why-is-there-colour/405849 "2007-05-29T01:43:53Z")\ **Posts on this page:** 17\ **Page:** 4
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 30, 2007, 5:40am UTC](https://boards.straightdope.com/t/why-is-there-colour/405849/61 "2007-05-30T05:40:29Z")
> [@](#): > > To get technical, rainbows really are a diffraction phenomenon. You can’t really understand things like supernumerary rainbows unless you use the wave nature of light. Well, some aspects of rainbows are diffractive. But isn’t the basic bow (without any supernumeraries) just a straight ray optics refraction? One can certainly model it as such. Of course, one can probably derive all of the ray optics phenomena as special cases of diffraction, since light is, after all, a wave. But I don’t think that it’s necessary, for a simple rainbow, in the same way that quantum mechanics isn’t necessary to describe a bat hitting a baseball. ---
**Author:** ![WarmNPrickly](https://avatars.discourse-cdn.com/v4/letter/w/d78d45/32.png) [@WarmNPrickly](https://boards.straightdope.com/u/WarmNPrickly)\ **Post date:** [May 30, 2007, 11:26am UTC](https://boards.straightdope.com/t/why-is-there-colour/405849/62 "2007-05-30T11:26:29Z")
[QUOTE=Christopher] Can you not make indigo from red and blue? Those color space diagrams seem to indicate that you can. [/QUOTE] I’ve been studying, the CIE 1931 color space and I can definitively say that no mixture of two spectral colors makes any other spectral color. They can only be approximated depending on the gamut defined by the spectral colors being used. How about that. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [May 30, 2007, 12:56pm UTC](https://boards.straightdope.com/t/why-is-there-colour/405849/63 "2007-05-30T12:56:12Z")
> [@](#): > > Well, some aspects of rainbows are diffractive. But isn’t the basic bow (without any supernumeraries) just a straight ray optics refraction? One can certainly model it as such. See my post – that’s why I went into it in some detail. Even the main bow is diffractive, in that the relative widths of the colors (or even whether those colors are _present_) depend upon the droplet size. As I say, Minnaert gives a cute table that lets you determine the size of the droplets making the rainbow, based solely upon the appearance of the bow (No yellow band? Then the droplets must be xx microns in diameter). So it’s not juast the appearance/lack of supernumerary bands that the droplet size affects. You CAN get the general width and location of the rainbow from pure geometrical optics, but as soon as you try to determine, say, relative intensity vs. angle, you run into the physical optics aspects of the rainbow. I only know about this (and bring it up) because I ran into this when I started correcting student reports on the rainbow, and discovered an entire aspect of meteorological optics that I never knew existed – yet it’s one which is over 150 years old, with some very nice well-worked math that’s worth looking at. It’s scandalous that this isn’t covered in physics and optics classes. ---
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [May 30, 2007, 8:37pm UTC](https://boards.straightdope.com/t/why-is-there-colour/405849/64 "2007-05-30T20:37:03Z")
**Q.E.D.** , you never responded to my last post. Did I crush you in the vice-like logic of my reply, or did you decide my ignorance was too profound to even bother to fight it? 😃 ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 31, 2007, 12:39am UTC](https://boards.straightdope.com/t/why-is-there-colour/405849/65 "2007-05-31T00:39:38Z")
I’m not sure what the misunderstanding is, frankly. I thought I was entirely clear on the matter. The perception of color as a general sense is dictated by wavelength; no argument there. However, the specific colors we perceive for each band of wavelengths is entirely arbitrary. There is no quality of what we see as red light that is inherently red, for example. We just happen to see it that way. ---
**Author:** ![Punoqllads](https://avatars.discourse-cdn.com/v4/letter/p/d2c977/32.png) [@Punoqllads](https://boards.straightdope.com/u/Punoqllads)\ **Post date:** [May 31, 2007, 1:25am UTC](https://boards.straightdope.com/t/why-is-there-colour/405849/66 "2007-05-31T01:25:17Z")
The fact is that most of us can distinguish red light from green light, but there are plenty of folks (5%?) that cannot. Maybe you feel that the computer colors 0xff0000 and 0x009900 look distinctly different, but there are quite a few gentlemen who would be left scratching their heads if you asked them to pick which one they preferred. Now compare us normal folks to the tetrachromats (1%?) out there. For us, a green from the television might look exactly the same as a green on our computer screen, but due to the difference in phosphers, a tetrachromat might see them as distinctly different. ---
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [May 31, 2007, 1:52am UTC](https://boards.straightdope.com/t/why-is-there-colour/405849/67 "2007-05-31T01:52:22Z")
[QUOTE=Q.E.D.] I’m not sure what the misunderstanding is, frankly. I thought I was entirely clear on the matter. The perception of color as a general sense is dictated by wavelength; no argument there. However, the specific colors we perceive for each band of wavelengths is entirely arbitrary. [/quote] Yeah, you said that before: > [@](#): > > Evolution basically assigned colors to various bands of wavelengths more or less randomly. That’s the definition of arbitrary. and I think that may be at the heart of our misunderstanding. Because the fact that we pretty much always see certain frequencies of light as the same colors (e.g., we never see the 620-700 nm range as blue) seems to me to be the definition of what “inherently red” means. Are you claiming that some other type of visual system would somehow perceive the wavelengths that we call red as the color we call blue? Or that evolution could have somehow arranged the visible spectrum to appear to go in the opposite direction? Or instead of ROY G BIV, it could have been GRIB YOV or BORG IVY? Why would you think that? Does your claim also apply to other senses? Is the sound of 440 Hz not “inherently” an A? Is this your own personal theory, **Q.E.D.** , or are you basing it on a source you could point me to? On preview: **Punoqllads** , is your post intended to support **Q.E.D.**'s position? If so, I don’t see the connection. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 31, 2007, 2:20am UTC](https://boards.straightdope.com/t/why-is-there-colour/405849/68 "2007-05-31T02:20:56Z")
> **[Introduction to Colour Science](http://www.techmind.org/colour/)** > > techmind.org - Colour perception > [@](#): > > Contrary to popular belief, “colour” is not really an intrinsic property of the things we see around us. Rather, it is the sensation resulting from a given spectral distribution of light, detected by the three colour-sensors in the eye and interpreted by the brain. ---
**Author:** ![WarmNPrickly](https://avatars.discourse-cdn.com/v4/letter/w/d78d45/32.png) [@WarmNPrickly](https://boards.straightdope.com/u/WarmNPrickly)\ **Post date:** [May 31, 2007, 2:23am UTC](https://boards.straightdope.com/t/why-is-there-colour/405849/69 "2007-05-31T02:23:20Z")
You can see a linear combination of 700nm light and 540nm light as yellow. How does that make sense in terms of wavelength? Why wouldnt you see it as red and green? Instead the combination can become remarkably close 570nm. That sort of perception doesn’t happen with sound. ---
**Author:** ![Punoqllads](https://avatars.discourse-cdn.com/v4/letter/p/d2c977/32.png) [@Punoqllads](https://boards.straightdope.com/u/Punoqllads)\ **Post date:** [May 31, 2007, 2:25am UTC](https://boards.straightdope.com/t/why-is-there-colour/405849/70 "2007-05-31T02:25:07Z")
Yes, it was intended to support **QED**. To compare it to an audio spectrum, suppose that a given sound might be someone playing two tones, one at 490 Hz and one at 560 Hz, at about the same volume level. Now suppose that someone else played three tones at once, one at 420 Hz, one at 600 Hz, and one at 500 Hz, at increasing levels of volume. For our perception of sound, those chords would sound distinctly different. However, for our eyes, the mixture of equal proportions of 490 nm and 560 nm light looks distinctly cerulian, as would an appropriate mixture of 420 nm, 600 nm, and 500 nm light. ---
**Author:** ![WarmNPrickly](https://avatars.discourse-cdn.com/v4/letter/w/d78d45/32.png) [@WarmNPrickly](https://boards.straightdope.com/u/WarmNPrickly)\ **Post date:** [May 31, 2007, 3:50am UTC](https://boards.straightdope.com/t/why-is-there-colour/405849/71 "2007-05-31T03:50:36Z")
I am actually suprised that **commasense** didn’t mention that the nature of sound and hearing means that it effectively does a qualitative Fourier transform on the incoming waves. With light however, the waves are so fast that such a transformation isn’t possible, so we see the combination. This is why I resorted to purple, in my previous argument. Apparently purple doesn’t exist. ---
**Author:** ![Malacandra](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Malacandra](https://boards.straightdope.com/u/Malacandra)\ **Post date:** [May 31, 2007, 10:05am UTC](https://boards.straightdope.com/t/why-is-there-colour/405849/72 "2007-05-31T10:05:03Z")
[QUOTE=Christopher] You can see a linear combination of 700nm light and 540nm light as yellow. How does that make sense in terms of wavelength? Why wouldnt you see it as red and green? Instead the combination can become remarkably close 570nm. That sort of perception doesn’t happen with sound. [/QUOTE] Of course it doesn’t, because our sound receptors aren’t wired that way. But our retinas don’t have a yellow receptor - they have a red, green and blue one. When you see yellow light (the true yellow that you could get from, say, a sodium spectral line) your blue receptors don’t notice it, and your red and green receptors react about equally. Your brain mixes the two signals together and reports “yellow”. But isn’t it obvious that if you also hit the eye with a combination of red and green light, exactly the same will happen? ---
**Author:** ![Punoqllads](https://avatars.discourse-cdn.com/v4/letter/p/d2c977/32.png) [@Punoqllads](https://boards.straightdope.com/u/Punoqllads)\ **Post date:** [May 31, 2007, 10:43am UTC](https://boards.straightdope.com/t/why-is-there-colour/405849/73 "2007-05-31T10:43:50Z")
Okay, yet more pedanticisim on my part. Your retinas do have a yellow receptor, but not a red receptor. The L cones of the average human observer peak at about 565 nm, which is yellow if not yellow-green in appearance. ---
**Author:** ![Malacandra](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Malacandra](https://boards.straightdope.com/u/Malacandra)\ **Post date:** [May 31, 2007, 12:13pm UTC](https://boards.straightdope.com/t/why-is-there-colour/405849/74 "2007-05-31T12:13:02Z")
[QUOTE=Punoqllads] Okay, yet more pedanticisim on my part. [/QUOTE] “Pedantry”. 😛😃🆒 ---
**Author:** ![WarmNPrickly](https://avatars.discourse-cdn.com/v4/letter/w/d78d45/32.png) [@WarmNPrickly](https://boards.straightdope.com/u/WarmNPrickly)\ **Post date:** [May 31, 2007, 1:15pm UTC](https://boards.straightdope.com/t/why-is-there-colour/405849/75 "2007-05-31T13:15:34Z")
[QUOTE=Christopher] With light however, the waves are so fast that such a transformation isn’t possible [/QUOTE] That idiot doesn’t know what he’s talking about. If we had a thousand different types of cones all with very narrow absorbtion bands we could have FT vision. It has nothing to do with the frequency of the waves. Idiot. ---
**Author:** ![Sapo](https://avatars.discourse-cdn.com/v4/letter/s/ec9cab/32.png) [@Sapo](https://boards.straightdope.com/u/Sapo)\ **Post date:** [May 31, 2007, 1:59pm UTC](https://boards.straightdope.com/t/why-is-there-colour/405849/76 "2007-05-31T13:59:40Z")
[QUOTE=Christopher] That idiot doesn’t know what he’s talking about. If we had a thousand different types of cones all with very narrow absorbtion bands we could have FT vision. It has nothing to do with the frequency of the waves. Idiot. [/QUOTE] This might be in violation of the “no insults” rule. Give yourself a warning before you have autoban yourself (unless you are driving in Germany). ---
**Author:** ![Kozmik](https://avatars.discourse-cdn.com/v4/letter/k/8dc957/32.png) [@Kozmik](https://boards.straightdope.com/u/Kozmik)\ **Post date:** [June 4, 2007, 2:15am UTC](https://boards.straightdope.com/t/why-is-there-colour/405849/77 "2007-06-04T02:15:46Z")
[QUOTE=CalMeacham] You need to read this Book: **The Physics and Chemistry of Color** by Kurt Nassau > **[Amazon.com: The Physics and Chemistry of Color: The Fifteen Causes of Color:...](https://www.amazon.com/Physics-Chemistry-Color-2nd/dp/0471391069)** > > Amazon.com: The Physics and Chemistry of Color: The Fifteen Causes of Color: 9780471391067: Nassau, Kurt: Books [/QUOTE] Another book you should read is Wittgenstein’s [Remarks on Colour](http://www.amazon.com/Remarks-Colour-Ludwig-Wittgenstein/dp/0520251792/ref=pd_bbs_sr_1/105-7883869-1999600?ie=UTF8&s=books&qid=1180922772&sr=1-1). [Previous page](https://boards.straightdope.com/t/why-is-there-colour/405849.md?page=3)