# Are the colours contiguous sections of the spectrum of visible light **URL:** \ **Category:** Factual Questions\ **Created:** [January 31, 2015, 5:29pm UTC](https://boards.straightdope.com/t/are-the-colours-contiguous-sections-of-the-spectrum-of-visible-light/711444 "2015-01-31T17:29:30Z")\ **Posts on this page:** 8\ **Page:** 2
**Author:** ![Precambrianmollusc](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/precambrianmollusc/32/63_2.png) [@Precambrianmollusc](https://boards.straightdope.com/u/Precambrianmollusc)\ **Post date:** [February 4, 2015, 4:18am UTC](https://boards.straightdope.com/t/are-the-colours-contiguous-sections-of-the-spectrum-of-visible-light/711444/21 "2015-02-04T04:18:54Z")
How the eye perceives colour can cause quite a few problems with data visualization. Say you have a range of 1,000 values ( eg height of a surface) and decide to use colour to represent height with the 1,000 increments split evenly across the regular spectrum of colours, weird things happen. What you will find is people see big 'changes ’ in the data where the data maps across the Blue / indigo / violet range and in the Yellow orange red transition, but data will look very ‘flat’ in the green band. Say you set height zero to be violet and ,10000 to be red, with all the mapping evenly spaced. A change from 200 to 400 would sweep you through moving from indigo to blue and appear to have a lot of change in height. The next change in height form 400 to 600 would all look green with almost no apparent transitions. You then get a sharp contrast form green to yellow, possible with minimal change in the underlaying data. Explained much better here > **[The rainbow is dead…long live the rainbow! – Perceptual palettes, part 1](https://mycartablog.com/2012/05/12/the-rainbow-is-dead-long-live-the-rainbow-part-1/)** > > Introduction This is the first  post in a series on the rainbow and similar color palettes. My goal is to demonstrate it is not a good idea to use these palettes to display scientific data, and the… Intro to his full series here > **[The rainbow is dead…long live the rainbow! – series outline](https://mycartablog.com/2012/05/29/the-rainbow-is-dead-long-live-the-rainbow-series-outline/)** > > The rainbow is dead…long live the rainbow! – Part 1 The rainbow is dead…long live the rainbow! – Part 2: a rainbow puzzle The rainbow is dead…long live the rainbow! – Part 3 The rainbow is dead…lon… And for those who like representing data with colour some excellent reasons not to use the normal rainbow spectral range, and if you are a MatLab kind of person, some great colour maps here. > **[Perceptually improved colormaps](https://www.mathworks.com/matlabcentral/fileexchange/28982-perceptually-improved-colormaps)** > > 7 perceptual colormaps with rainbow-like colors and 1 with heat colors ---
**Author:** ![thelurkinghorror](https://avatars.discourse-cdn.com/v4/letter/t/7c8e57/32.png) [@thelurkinghorror](https://boards.straightdope.com/u/thelurkinghorror)\ **Post date:** [February 4, 2015, 4:31am UTC](https://boards.straightdope.com/t/are-the-colours-contiguous-sections-of-the-spectrum-of-visible-light/711444/22 "2015-02-04T04:31:53Z")
> [@Francis\_Vaughan](#): > > Yes, I was referring to the matching functions. Although there is no physical realisation inside the body of these curves, they are the easiest to understand in thinking about how colours work. > > The bump does come from the cone’s sensitivity, but is hard to see when you look at the curves. Whilst it is true the cones have a single peak each, what matters is the difference in sensitivities between them, and at the blue end you see that the difference between the sensitivities has a glitch - both red and blue are dropping down towards zero, but the red sensitivity shallows out slightly, and thus the difference between red and blue is less, with the result that the effective processed colour information has the bump in it. Right, just as long as it is certain that the L cone itself is not sensitive to blue. > [@Mijin](#): > > Another feature of our colour vision is that there are two ways to make yellow. > It exists as both a discrete wavelength of EM radiation, and also can be made by combining red and green frequency light. > > This is a quirk of how our colour vision works. If we had fully 3 degrees of freedom of colour vision red and green should make another colour. > [This link](http://blog.asmartbear.com/color-wheels.html) gives a nice intro (towards the end explaining about yellow), and at the very bottom there’s a link to much more information than you could ever possibly want about human colour vision. Sorry, I don’t see what that link means or that there is anything special with yellow. Yes you can make yellow (at least but many more than) two ways, but the same is true of cyan, orange, chartreuse, or puce. Two colors [can be perceived the same but completely spectrally different](http://en.wikipedia.org/wiki/Metamerism_%28color%29). Yellow is not special. ‘Every seven-year-old kid in America is taught that “the opposite of red is green” and “the opposite of blue is yellow.”’ I remember 7+/-2 year old **tlh** making drawings where red was opposed to green; blue and orange; yellow and purple. When you have a three-primary system, there is no opposite color unless you go into the secondary colors that are a combination of 2/3 of the primaries (r+y=o; r+b=p; y+b=g). So those seven year olds are essentially wrong. Dumb kids :D. RBY vs. CMY is a rather arbitrary distinction. The part about the “filters,” i.e. the ganglion cell layer of the retina and LGN leading to the opponent colors - if you look at color spaces, it is not unintuitive to see how R+G = yellow signal, in the absence of blue. BTW, Filter #3 is essentially not correct: due to a biological quirk the S/blue cones don’t contribute much to our intensity perception. L/M cones are essentially identical except for their sensitivities, whereas S cones are sparser on the retina, in different areas, coarser resolution, and encoded on a separate chromosome. So the differences are much larger and they do not work well without the others. The last section on color constancy occurs further on; in the cortex. Essentially our perception is a result of complex calculations in our brain, that get input from simpler cortical calculations, that get input from lower brain areas, that get input from our retina. So we can look at what the cones are doing, but it doesn’t translate directly, without tons of intermediate steps, to our perception. ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [February 4, 2015, 5:25am UTC](https://boards.straightdope.com/t/are-the-colours-contiguous-sections-of-the-spectrum-of-visible-light/711444/23 "2015-02-04T05:25:37Z")
> [@thelurkinghorror](#): > > Sorry, I don’t see what that link means or that there is anything special with yellow. Yes you can make yellow (at least but many more than) two ways, but the same is true of cyan, orange, chartreuse, or puce. Two colors [can be perceived the same but completely spectrally different](http://en.wikipedia.org/wiki/Metamerism_%28color%29). Yellow is not special. There are similar “filters”, in the ganglion cell layer of the retina, for puce? ---
**Author:** ![thelurkinghorror](https://avatars.discourse-cdn.com/v4/letter/t/7c8e57/32.png) [@thelurkinghorror](https://boards.straightdope.com/u/thelurkinghorror)\ **Post date:** [February 4, 2015, 5:38am UTC](https://boards.straightdope.com/t/are-the-colours-contiguous-sections-of-the-spectrum-of-visible-light/711444/24 "2015-02-04T05:38:19Z")
> [@Mijin](#): > > There are similar “filters”, in the ganglion cell layer of the retina, for puce? No, but depending on how you define it, there is either exactly one way to make yellow, or there are many, many ways. As part of the EM spectrum, it has no meaning except as how we perceive it as a color. When we reach color opponency, the spectral information is essentially lost and we only have relative activation. But comparing them is apples and oranges. ---
**Author:** ![Cartoonacy](https://avatars.discourse-cdn.com/v4/letter/c/848f3c/32.png) [@Cartoonacy](https://boards.straightdope.com/u/Cartoonacy)\ **Post date:** [February 5, 2015, 11:29pm UTC](https://boards.straightdope.com/t/are-the-colours-contiguous-sections-of-the-spectrum-of-visible-light/711444/25 "2015-02-05T23:29:13Z")
> [@The\_Hamster\_King](#): > > Magenta is a mixture of low and high wavelengths. It does not exist as a single wavelength on the visible spectrum. My point exactly. ---
**Author:** ![Schnitte](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/schnitte/32/9033_2.png) [@Schnitte](https://boards.straightdope.com/u/Schnitte)\ **Post date:** [February 8, 2015, 2:54pm UTC](https://boards.straightdope.com/t/are-the-colours-contiguous-sections-of-the-spectrum-of-visible-light/711444/26 "2015-02-08T14:54:56Z")
> [@Sage\_Rat](#): > > As one piece of evidence, if the colors weren’t contiguous, there would be a transparent band in the rainbow. I´m aware of that; my question concerned the _names_ we give to the colours. I was wondering whether there are non-adjacent parts of the rainbow spectrum that are commonly referred to by the same name. ---
**Author:** ![Cartoonacy](https://avatars.discourse-cdn.com/v4/letter/c/848f3c/32.png) [@Cartoonacy](https://boards.straightdope.com/u/Cartoonacy)\ **Post date:** [February 9, 2015, 8:50pm UTC](https://boards.straightdope.com/t/are-the-colours-contiguous-sections-of-the-spectrum-of-visible-light/711444/27 "2015-02-09T20:50:45Z")
> [@Schnitte](#): > > I´m aware of that; my question concerned the _names_ we give to the colours. I was wondering whether there are non-adjacent parts of the rainbow spectrum that are commonly referred to by the same name. That _is_ an interesting question. I don’t believe that there are any in the English language. Regarding other languages, according to [the research of Paul Kay and Luisa Maffi](http://wals.info/chapter/133), there are languages that have a single word to describe red and yellow, or blue/green, or yellow/green, or yellow/green/blue, but in each of these cases the colors are adjacent in the spectrum. Some languages, they say, have a single word for Black/Green/Blue, White/Red/Yellow, or Black/Blue, but since black and white aren’t spectral colors then they’re irrelevant to the question. ---
**Author:** ![thelurkinghorror](https://avatars.discourse-cdn.com/v4/letter/t/7c8e57/32.png) [@thelurkinghorror](https://boards.straightdope.com/u/thelurkinghorror)\ **Post date:** [February 9, 2015, 9:59pm UTC](https://boards.straightdope.com/t/are-the-colours-contiguous-sections-of-the-spectrum-of-visible-light/711444/28 "2015-02-09T21:59:03Z")
> [@Cartoonacy](#): > > That _is_ an interesting question. I don’t believe that there are any in the English language. Regarding other languages, according to [the research of Paul Kay and Luisa Maffi](http://wals.info/chapter/133), there are languages that have a single word to describe red and yellow, or blue/green, or yellow/green, or yellow/green/blue, but in each of these cases the colors are adjacent in the spectrum. Some languages, they say, have a single word for Black/Green/Blue, White/Red/Yellow, or Black/Blue, but since black and white aren’t spectral colors then they’re irrelevant to the question. Regarding the WCS, and maybe not a direct answer to the OP (as it is Munsell not spectrum, although terms are adjacent from what I can tell and I hope it helps): they ask two basic questions. 1) Given [an array of color chips](http://www.innerfictions.com/images/color/wcs-stimulus.jpg), what is the “best” blue (green/red/etc.), and 2) For each of these chips, what color is it. This gives us a rough analogy of central tendency and variability. For example, [English](http://www.innerfictions.com/images/color/wcs-gen.jpg). [Previous page](https://boards.straightdope.com/t/are-the-colours-contiguous-sections-of-the-spectrum-of-visible-light/711444.md?page=1)