# Colors - primary vs. secondary and the rainbow **URL:** \ **Category:** Factual Questions\ **Created:** [March 21, 2015, 7:30pm UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627 "2015-03-21T19:30:27Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![crypto](https://avatars.discourse-cdn.com/v4/letter/c/b3f665/32.png) [@crypto](https://boards.straightdope.com/u/crypto)\ **Post date:** [March 23, 2015, 2:37am UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627/21 "2015-03-23T02:37:27Z")
> [@Martian Bigfoot](#): > > Also, unlike your color wheel, there’s nothing “circular” about the rainbow or the electromagnetic spectrum. If you mix red and blue in your artist’s color wheel, you get a purple color that your brain interprets as looking more or less the same as the violet end of the spectrum. But this is your brain (and the color receptors in your eyes) playing tricks. It’s an optical illusion. The wavelengths corresponding to violet is way on the other side of the visible spectrum from red. They don’t meet up, they just bugger off into ultraviolet and infrared. I understand the “color wheel” is a man-made concept, and that red and violet never meet in the light spectrum. They are just the beginning and end of the visible color spectrum, seen in a rainbow. I was just referring to how it could be better represented as a concept if 6 colors were used, and not 7. The “color wheel”, while incorrect from a light wavelength POV, would show the correct color between red and blue. However, you have a point. Let’s take the color wheel out of this discussion, and just punt indigo! “No Pluto, no Indigo!” (Bumper stickers and t-shirts will be available soon in the gift shop). ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [March 23, 2015, 4:30am UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627/22 "2015-03-23T04:30:56Z")
> [@Martian Bigfoot](#): > > Also, unlike your color wheel, there’s nothing “circular” about the rainbow or the electromagnetic spectrum. [A circular rainbow.](http://a.abcnews.com/images/International/cn_round_rainbow_australia_jc_141010_16x9_992.jpg) ---
**Author:** ![Don\_t\_Panic](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/don_t_panic/32/398_2.png) [@Don\_t\_Panic](https://boards.straightdope.com/u/Don_t_Panic)\ **Post date:** [March 23, 2015, 4:33am UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627/23 "2015-03-23T04:33:12Z")
> [@Senegoid](#): > > [A circular rainbow.](http://a.abcnews.com/images/International/cn_round_rainbow_australia_jc_141010_16x9_992.jpg) Good point. Maybe I should have phrased that more precisely. 😛 ---
**Author:** ![Hermitian](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hermitian/32/470_2.png) [@Hermitian](https://boards.straightdope.com/u/Hermitian)\ **Post date:** [March 23, 2015, 1:56pm UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627/24 "2015-03-23T13:56:09Z")
There’s something I need to get off my chest guys. Many years ago I was attending “trivia night” at Rockhoppers restaurant. The trivia hostess asked the question, “What are the three primary colors.” I said red, green, and blue. The trivia hostess later announced it was red, yellow, and blue. I approached her about this answer, but she basically called me an idiot and said every first grader knows its red, yellow, and blue. I’m still ticked 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:** [March 23, 2015, 2:44pm UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627/25 "2015-03-23T14:44:04Z")
I devote a chapter in my book to precisely the topic of why there are seven colors in the rainbow. The short answer – it’s Newton’s And Newton really is the first person to suggest there are seven colors in the rainbow fault, but not because of the “mystical” properties of the number seven. In his first draft of _Opticks_ Newton talked about only FIVE colors in the rainbow, and he wasn’t scrupulous about changing things, so those passages are still in there, alongside ones that talk about seven colors. The two he left out were orange and indigo. What seems to have c hanged his mind was his seeing the analogy to the musical scale. Although Newton didn’t believe in the wave nature of light, he definitely associated characteristic lengths with the colors. You can see this in his treatmernt of the phenomenon called “Newton’s rings”, where he saw interference effects between light reflected from a spherical glass surface placed on a flat glass surface. He could calculate the distances between the surfaces and associate it with the color (although, not believing in waves, he didn’t see this as wave interference). What’s more, after you went through one series of colors, it would repeat with another set of colors, and then another. It was just like the way the notes on a piano go from one octave to another, from C through D, E, F,G, A, and B back to the C and octave higher. On a piano or a harp, the tone of the note was associated with the length, and in classical tuning there are distinct mathematical relationshiops between the notes"D" uses a string 8/9 as long as “c” in classical tempering, “E” is 3/4 as long, and so on, until a string half as long gives you the “C” of the next octave. Well, Newton had lengths associated with the colors, so he compared those with the ratios for musical notes and – _mirabile dictum_ – they were the same! Only now he hade a problem with his five color spectrum, because there are seven distinct notes in the octave, ignoring the top note C, D, E, F. G. A, and B, ignoring the upper C. Or Do Re Mi Fa Sol La Ti (and then to the next “do”) (You can stop singing “Doe, a Deer” in your head now.) Newton’s use of five colors oprobably comes fro his looking at the interference phenomenon of Newton’s Rings in white light, for which the orange isn’t so obvious and indigo is part of that whole bluie-violet run. So he looked at light from his prism, or from the rainbow, and realized , while red and yellow fit pretty well for lower “Do” and “Mi”, he needed a different color for “re”. Well, that was yellow in his prism-produced spectrum. He had a harder time with “La”, which had to fall between blue and violet. To me, I don’t see a different named color in there. But Newton decided there was, and called it “Indigo”, and interviewed his friends, trying to get them to agree that “indigo” was really, really a different color than blue. I’ll bet this made him even less popular than he already was. “Indigo” is the plant coloring that makes blue jeans blue. There’s a reason we don’t call them “indigo jeans”. Most people just don’t see the difference. If you look at those “rainbow” flags, you;'ll notice that they either only have six colors (no indigo), or else substitute a light blue (which DERFINITELY isn’t indigo) for the seventh. [https://images.search.yahoo.com/images/view;\_ylt=AwrB8qHuJRBVEBIAbl.JzbkF;\_ylu=X3oDMTIyMmYzYXNoBHNlYwNzcgRzbGsDaW1nBG9pZANkZGY0YzI3YTUwOTFlMDI2NzZhNjYyODgwODljNTg5NgRncG9zAzEEaXQDYmluZw--?.origin=&back=https%3A%2F%2Fimages.search.yahoo.com%2Fsearch%2Fimages%3Fp%3DRainbow%2BFlag%26fr%3Dyfp-t-252%26tab%3Dorganic%26ri%3D1&w=1024&h=768&imgurl=images.kaneva.com%2Ffilestore7%2F3839926%2F4675378%2Frainbow\_flag\_1024\_768.jpg&rurl=http%3A%2F%2Fwww.kaneva.com%2Fmykaneva%2FPictureDetail.aspx%3FassetId%3D4675378&size=23.7KB&name=\rainbow+flag\<%2Fb\>+uploaded+by+kishkasayshello+on+Sunday%2C+April+13%2C+2008&p=Rainbow+Flag&oid=ddf4c27a5091e02676a66288089c5896&fr2=&fr=yfp-t-252&tt=\rainbow+flag\<%2Fb\>+uploaded+by+kishkasayshello+on+Sunday%2C+April+13%2C+2008&b=0&ni=288&no=1&ts=&tab=organic&sigr=121jatt79&sigb=12q06i520&sigi=126053otr&sigt=1292njaj7&sign=1292njaj7&.crumb=iFnxBO8CwGG&fr=yfp-t-252](https://images.search.yahoo.com/images/view;_ylt=AwrB8qHuJRBVEBIAbl.JzbkF;_ylu=X3oDMTIyMmYzYXNoBHNlYwNzcgRzbGsDaW1nBG9pZANkZGY0YzI3YTUwOTFlMDI2NzZhNjYyODgwODljNTg5NgRncG9zAzEEaXQDYmluZw--?.origin=&back=https%3A%2F%2Fimages.search.yahoo.com%2Fsearch%2Fimages%3Fp%3DRainbow%2BFlag%26fr%3Dyfp-t-252%26tab%3Dorganic%26ri%3D1&w=1024&h=768&imgurl=images.kaneva.com%2Ffilestore7%2F3839926%2F4675378%2Frainbow_flag_1024_768.jpg&rurl=http%3A%2F%2Fwww.kaneva.com%2Fmykaneva%2FPictureDetail.aspx%3FassetId%3D4675378&size=23.7KB&name=%3Cb%3Erainbow+flag%3C%2Fb%3E+uploaded+by+kishkasayshello+on+Sunday%2C+April+13%2C+2008&p=Rainbow+Flag&oid=ddf4c27a5091e02676a66288089c5896&fr2=&fr=yfp-t-252&tt=%3Cb%3Erainbow+flag%3C%2Fb%3E+uploaded+by+kishkasayshello+on+Sunday%2C+April+13%2C+2008&b=0&ni=288&no=1&ts=&tab=organic&sigr=121jatt79&sigb=12q06i520&sigi=126053otr&sigt=1292njaj7&sign=1292njaj7&.crumb=iFnxBO8CwGG&fr=yfp-t-252) [https://search.yahoo.com/search;\_ylt=AuqobCFe405EOzUCx7gQKyKbvZx4?p=Rainbow+flag+image&toggle=1&cop=mss&ei=UTF-8&fr=yfp-t-252&fp=1](https://search.yahoo.com/search;_ylt=AuqobCFe405EOzUCx7gQKyKbvZx4?p=Rainbow+flag+image&toggle=1&cop=mss&ei=UTF-8&fr=yfp-t-252&fp=1) Similarly, the Universal Code for resistors mainly uses the spectral colors, in order, but pointedly skips “indigo” > **[Electronic color code](https://en.wikipedia.org/wiki/Electronic_color_code)** > > An electronic color code or electronic colour code (see spelling differences) is used to indicate the values or ratings of electronic components, usually for resistors, but also for capacitors, inductors, diodes and others. A separate code, the 25-pair color code, is used to identify wires in some telecommunications cables. Different codes are used for wire leads on devices such as transformers or in building wiring. > > Before industry standards were established, each manufacturer used their o... There are, of course, virtually infinite gradations across the spectrum. We simply don’t try to name them all. It’s a good thing that Newton didn’t take the full chromatic scale as his model – using the black keys as well as the white keys, or else we’d need five more color names, with another, for instance, between red and orange. Tangerine? Sunburn? Rust? ---
**Author:** ![swampspruce](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/swampspruce/32/261_2.png) [@swampspruce](https://boards.straightdope.com/u/swampspruce)\ **Post date:** [March 23, 2015, 3:51pm UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627/26 "2015-03-23T15:51:32Z")
So has anyone taken a stab at presenting music visually with each colour represented by a note? Combine that with a [lissajous generator](http://www.atatan.com/a/hard/kitz01.html) and I think it might be worthy of a laser show… [http://homepage.tinet.ie/~musima/visualmusic/visualmusic.htm](http://homepage.tinet.ie/~musima/visualmusic/visualmusic.htm) ---
**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:** [March 23, 2015, 5:39pm UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627/27 "2015-03-23T17:39:49Z")
> [@swampspruce](#): > > So has anyone taken a stab at presenting music visually with each colour represented by a note? > Combine that with a [lissajous generator](http://www.atatan.com/a/hard/kitz01.html) and I think it might be worthy of a laser show… > > [Visual Music](http://homepage.tinet.ie/~musima/visualmusic/visualmusic.htm) Not as far as I know. I’ve considered the possibility of a Rainbow symphony, but lack the musical chops to compose one. When Philip Morison did his PBS series “The Ring of Truth” back in 1993, he explained the different colors as having different wavelengths while sitting at a piano keyboard that had the keys of the octave at middle C painted in the colors of the spectrum as a clever way to illustrate the concept. I don’t know if he was aware of Newton’s derriving his colors on the same basis, but it’s the closest I’ve seen to anyone drawing the analogy between music and color, and playing an instrument at the time. ---
**Author:** ![chrisk](https://avatars.discourse-cdn.com/v4/letter/c/6de8d8/32.png) [@chrisk](https://boards.straightdope.com/u/chrisk)\ **Post date:** [March 23, 2015, 6:02pm UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627/28 "2015-03-23T18:02:07Z")
Okay, since I posted in this thread last I think I’ve come up for a rationale why there should be seven colors in the visible spectrum; not necessarily the classical seven, but still seven: There are typically three kinds of color-sensitive cones in the human eye. If you map sensitivity of each versus wavelength, you’ll get three rough bell curves A B & C, each overlapping with the curve next to it at least. The A and C curves might also overlap a little, but that’s not really important. Assign one named color to the highest point on each curve. That’s three. Assign named colors to the range where A and B are approximately equally sensitive, and similarly where B and C intersect. That’s two more, total of five. Finally, assigned named colors to the “outer slopes” of curves A and C, where they’re still sensitive but the furthest from any other color. That gives us a total of seven. But when we try to assign names, the two reddest colors become problematic. Do we make the peak of the red-cone curve “Red” and use “Maroon” or “Rust” or something else for the part of the spectrum where red shades to infra-red? Or use “red” for the reddest and “orange” for the peak of the red sensitivity? Then you’d have yellow, green, aquamarine/turquoise/cyan, blue, and violet. ---
**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:** [March 23, 2015, 6:12pm UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627/29 "2015-03-23T18:12:25Z")
> [@chrisk](#): > > Okay, since I posted in this thread last I think I’ve come up for a rationale why there should be seven colors in the visible spectrum; not necessarily the classical seven, but still seven: > > There are typically three kinds of color-sensitive cones in the human eye. If you map sensitivity of each versus wavelength, you’ll get three rough bell curves A B & C, each overlapping with the curve next to it at least. The A and C curves might also overlap a little, but that’s not really important. > > Assign one named color to the highest point on each curve. That’s three. > > Assign named colors to the range where A and B are approximately equally sensitive, and similarly where B and C intersect. That’s two more, total of five. > > Finally, assigned named colors to the “outer slopes” of curves A and C, where they’re still sensitive but the furthest from any other color. That gives us a total of seven. > > But when we try to assign names, the two reddest colors become problematic. Do we make the peak of the red-cone curve “Red” and use “Maroon” or “Rust” or something else for the part of the spectrum where red shades to infra-red? Or use “red” for the reddest and “orange” for the peak of the red sensitivity? > > Then you’d have yellow, green, aquamarine/turquoise/cyan, blue, and violet. You can come up with any sort of reason you want, but “classical” seven, as I say, only goes back to Newton. There have been other color numberings in the past – 4 or 5, but the only other ones to posit seven colors were Medieval artist Cennino Cennini (whose seven colors included White and Black, which we wouldn’t call “colors”) and 16th century theorist Franciscus Maurolycus, but I distrust the evidence in his case. Newton, as I say, chose his by analogy with musical tones. But there’s really no reason for choosing any number of colors – they don’t have to align with the number of distinct color sensors in our eye or the number of their intersections. Choose ten equally-spaced colors from least to most sensitive, if you wish. ---
**Author:** ![Don\_t\_Panic](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/don_t_panic/32/398_2.png) [@Don\_t\_Panic](https://boards.straightdope.com/u/Don_t_Panic)\ **Post date:** [March 23, 2015, 7:35pm UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627/30 "2015-03-23T19:35:11Z")
> [@chrisk](#): > > Okay, since I posted in this thread last I think I’ve come up for a rationale why there should be seven colors in the visible spectrum; not necessarily the classical seven, but still seven […] This post is freaking brilliant. If you can get on board with making the two red colors red and orange, then we have the scientific rationale in place for the Red-Orange-Yellow-Green-Cyan-Blue-Violet revolution. Roy G. Cbv says: No indigo! I’ll start making the flyers and printing the T-shirts. ---
**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:** [March 23, 2015, 10:14pm UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627/31 "2015-03-23T22:14:35Z")
> [@](#): > > Quoth **Stink Fish Pot** : > > I wonder… Why has there been no change in the identification of the colors of the “rainbow” since Newton? Is it because Newton is credited with the identification and naming of the seven colors we all know now, and questioning/altering anything Newton came up with is sacrilege? Is it just tradition? Who says there hasn’t been? I learned ROYGBP in kindergarten, if not earlier, and didn’t hear of this funny “indigo” thing until high school. I expect many other folks have had the same experience. Is what one learns in high school necessarily “more official” than what one learns in kindergarten? If anything, I’d be inclined to argue the opposite. ---
**Author:** ![cmyk](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmyk/32/3353_2.png) [@cmyk](https://boards.straightdope.com/u/cmyk)\ **Post date:** [March 23, 2015, 11:37pm UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627/32 "2015-03-23T23:37:24Z")
> [@pulykamell](#): > > [RYB](http://en.wikipedia.org/wiki/RYB_color_model) is a set of primary colors. It’s just not the one with the widest gamut for subtractive color mixing. Right, which is why it’s a shame it’s still taught to students when we know better, and such pigments are not only readily available, but a standard in color reproduction. CMY is a huge improvement over RYB. > [@Martian Bigfoot](#): > > …BTW, another fun optical illusion: Magenta, a primary color in your friendly CMYK model, isn’t even in the rainbow. It’s a non-spectral color, and doesn’t correspond to a specific wavelength of light. In a sense it exists only in your brain. (Although I’m note sure if you should mention that to **cmyk** , he may get some existential angst…) It’s something I’ve come to accept. 😉 But hey… All the colors only really exist in our brain. ---
**Author:** ![Don\_t\_Panic](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/don_t_panic/32/398_2.png) [@Don\_t\_Panic](https://boards.straightdope.com/u/Don_t_Panic)\ **Post date:** [March 24, 2015, 5:56am UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627/33 "2015-03-24T05:56:12Z")
> [@swampspruce](#): > > So has anyone taken a stab at presenting music visually with each colour represented by a note? For something like the opposite of that, the rainbow (plus some colors that we can’t even see) illustrated with sound, check out [this Radiolab episode](http://www.radiolab.org/story/211178-rip-rainbow/). Skip to around 9:30 for the action, and more fun facts than you ever knew that you needed to know about the amazing mantis shrimp. ---
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [March 24, 2015, 4:00pm UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627/34 "2015-03-24T16:00:46Z")
For a long time, I’ve assumed that using “blue, indigo” in the traditional color spectrum names indicated linguistic drift. That what they used to call “blue”, we now call “cyan”, and what they used to call “indigo” we now call “blue”. That is, the primary color word “blue” has drifted away from green and toward violet. Based on what **CalMeacham** says on Newton being the originator of the English terms, my assumption is probably wrong. Personally, I consider there to be six colors in the rainbow: red, yellow, green, cyan, blue, violet. “Orange” is too narrow to be useful, and “indigo” is too archaic. Do other languages have a well-defined set of “rainbow colors”, traditional or not? ---
**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:** [March 24, 2015, 4:45pm UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627/35 "2015-03-24T16:45:12Z")
> [@Pleonast](#): > > For a long time, I’ve assumed that using “blue, indigo” in the traditional color spectrum names indicated linguistic drift. That what they used to call “blue”, we now call “cyan”, and what they used to call “indigo” we now call “blue”. That is, the primary color word “blue” has drifted away from green and toward violet. Based on what **CalMeacham** says on Newton being the originator of the English terms, my assumption is probably wrong. > > Personally, I consider there to be six colors in the rainbow: red, yellow, green, cyan, blue, violet. “Orange” is too narrow to be useful, and “indigo” is too archaic. > > Do other languages have a well-defined set of “rainbow colors”, traditional or not? I don’t know how “well defined:” they are in other cultures or languages. The Wikipedia article in English doesn’t say, but the French edition claims that the number of colors seen varies between 3 and 9: > [@](#): > > Le nombre des couleurs varie de 3 à 9 selon les cultures. Aristote discernait trois couleurs2, Plutarque en mentionne quatre3. Aujourd’hui en Occident, les représentations ont souvent six ou sept couleurs. > **[Arc-en-ciel](https://fr.wikipedia.org/wiki/Arc-en-ciel)** > > Pour les articles homonymes, voir Arc-en-ciel (homonymie). > Un arc-en-ciel est un photométéore — un phénomène optique se produisant dans le ciel — visible dans la direction opposée au Soleil quand il brille pendant la pluie. C'est un arc de cercle coloré d'un dégradé de couleurs. > Un arc-en-ciel se compose de deux arcs principaux : l'arc primaire et l'arc secondaire. L'arc primaire est dû aux rayons ayant effectué une réflexion interne dans la goutte d'eau. Les couleurs se succèdent du rouge à l'... I’ll have to look into my copy of Boyer when I get home and see what he says. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [March 24, 2015, 10:05pm UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627/36 "2015-03-24T22:05:17Z")
> [@chrisk](#): > > Okay, since I posted in this thread last I think I’ve come up for a rationale why there should be seven colors in the visible spectrum; not necessarily the classical seven, but still seven: > > There are typically three kinds of color-sensitive cones in the human eye. If you map sensitivity of each versus wavelength, you’ll get three rough bell curves A B & C, each overlapping with the curve next to it at least. The A and C curves might also overlap a little, but that’s not really important. > > Assign one named color to the highest point on each curve. That’s three. > > Assign named colors to the range where A and B are approximately equally sensitive, and similarly where B and C intersect. That’s two more, total of five. > > **Finally, assigned named colors to the “outer slopes” of curves A and C, where they’re still sensitive but the furthest from any other color. That gives us a total of seven.** > > But when we try to assign names, the two reddest colors become problematic. Do we make the peak of the red-cone curve “Red” and use “Maroon” or “Rust” or something else for the part of the spectrum where red shades to infra-red? Or use “red” for the reddest and “orange” for the peak of the red sensitivity? > > Then you’d have yellow, green, aquamarine/turquoise/cyan, blue, and violet. Actually, IIRC from an earlier thread, in fact the red cone sensor in addition to primary red sensitivity has a slight sensitivity “hump” past the blue cone sensitivity, which is why we perceive violet/purple/whatever as a separate colour that appears to be a combination of blue and red. ---
**Author:** ![Don\_t\_Panic](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/don_t_panic/32/398_2.png) [@Don\_t\_Panic](https://boards.straightdope.com/u/Don_t_Panic)\ **Post date:** [March 24, 2015, 10:12pm UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627/37 "2015-03-24T22:12:58Z")
> [@md2000](#): > > Actually, IIRC from an earlier thread, in fact the red cone sensor in addition to primary red sensitivity has a slight sensitivity “hump” past the blue cone sensitivity, which is why we perceive violet/purple/whatever as a separate colour that appears to be a combination of blue and red. Right. If you look at the wavelengths, the violet part of the visible spectrum should just be more blue. But very blue wavelengths also pop the red sensor some, and your brain basically imagines that the color has red in it. It’s a bug in the system. It’s a lovely bug, though. Lovely enough to call it feature. 😛 ---
**Author:** ![crypto](https://avatars.discourse-cdn.com/v4/letter/c/b3f665/32.png) [@crypto](https://boards.straightdope.com/u/crypto)\ **Post date:** [March 24, 2015, 10:49pm UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627/38 "2015-03-24T22:49:03Z")
> [@Chronos](#): > > Who says there hasn’t been? I learned ROYGBP in kindergarten, if not earlier, and didn’t hear of this funny “indigo” thing until high school. I expect many other folks have had the same experience. Is what one learns in high school necessarily “more official” than what one learns in kindergarten? If anything, I’d be inclined to argue the opposite. I am not sure I understand this reply. According to the folks in this thread (and wikipedia, where all truth is revealed!) newton went with 7 colors. The fact that you learned ROYGBP in kindergarten is fine with me, but if I were to guess (and I am!), your teacher presented a concept that, quite frankly, is simpler to understand. It also stops 5 year olds from asking their teacher why their 8-pack of crayolas doesn’t have an “indigo” crayon, or what in the world indigo is, anyway? I don’t know if you were bothered by my question, or I’ve been “wooshed”, but as far as I can tell, this Newton fellow decided initially that there were 5 colors, then thought about it and tried to make a connection to the musical scale and TADA! 7 colors! tldr - see **CalMeacham’s** post a bit upthread. ---
**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:** [March 24, 2015, 11:00pm UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627/39 "2015-03-24T23:00:09Z")
Well, yes, it’s still the case that Newton said that there were seven. That’s never going to change, unless we find some lost manuscript of his. But I’m saying that most people nowadays don’t actually consider what Newton said to be official. Kindergarteners don’t know indigo. Small boxes of crayons don’t include indigo. Rainbow flags usually don’t include indigo. It looks to me like the question “When will the identification of the colors of the rainbow change” is answered perfectly well by “it already has”. ---
**Author:** ![pulykamell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pulykamell/32/3166_2.png) [@pulykamell](https://boards.straightdope.com/u/pulykamell)\ **Post date:** [March 24, 2015, 11:16pm UTC](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627/40 "2015-03-24T23:16:22Z")
> [@Pleonast](#): > > For a long time, I’ve assumed that using “blue, indigo” in the traditional color spectrum names indicated linguistic drift. That what they used to call “blue”, we now call “cyan”, and what they used to call “indigo” we now call “blue”. That is, the primary color word “blue” has drifted away from green and toward violet. Based on what **CalMeacham** says on Newton being the originator of the English terms, my assumption is probably wrong. That’s an interesting question I’ve been wondering about myself. I’ve learned ROY G BIV from primary school (never heard ROYGBP myself), but when I look at online graphic (non-photographic) representations of the rainbow, I find a lot that I would call closer to ROY G CBV, with “cyan” being “blue” and “blue” being “indigo.” I wonder if there’s been some drift in the definition of cyan and blue. For example, there’s a common paint color called “cerulean blue,” which is closer, in my opinion, to cyan than it is to blue. And what do people think of the description of “purple” vs “violet”? To me, “purple” has more of a reddish component, and “violet” has more a bluish component. [Previous page](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627.md?page=1) [Next page](https://boards.straightdope.com/t/colors-primary-vs-secondary-and-the-rainbow/715627.md?page=3)