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When people are asked to match monchromatic violet light with an additive mix of basic colours, they (paradoxically) mix in red. In fact, the CIE 1931 color space chromaticity diagram shows this effect begins at about 510nm (greenish-cyan), where people mix in no red. From that point on, the higher the frequency of the light source, the more red they mix in.

This effect is reflected by the red curve of the CIE standard observer color matching functions, which has an additional bump in the area of blue light. However, that curve does not match the actual spectral sensitivity of red cones. So where does this additional perception of red at higher frequencies come from?

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It's probably because the red absorption curve is very broad, not because of a double-bump, but I don't know for sure, and I wouldn't know where to look it up. – Ron Maimon Oct 15 '12 at 5:30
math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html There is a double bump on the second picture. There is some inconsistency in data, Some sources indicate that there are double bumps, some dont. I dont know what to make of it – Prathyush Oct 15 '12 at 18:41
I don't think this has a purely physical explanation. I think it's a fact about psychophysics, not the physics of retinal cells and their pigments. For comparison, the sound spectrum is linear, but there is a psychological phenomenon of octave identification, which makes the spectrum "wrap around," so that frequencies f and 2f are perceptually similar and can often be mistaken for one another even by trained musicians. Octave identification is innate, not learned. I don't know for sure, but I suspect the color wheel is exactly analogous. – Ben Crowell May 3 at 18:14

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It's pretty hard to research but I think (not sure) that the short-wavelength spectra may appear deep violet because of a negative green cone response. This answer also explains the apparent brightness of violet.

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Edit3: Since several people have pointed out that the sources in Wikipedia and articles linked are unscientific therefore Invalid. I have removed them.

The question needs a Graph of the sensitivity of the Red cone cells. This is the best I could find, It points to the paper where it is taken from, and the method by which it was measured. If you are interested Look into the paper.

http://www.yorku.ca/eye/specsens.htm

The correctness of the data in this Graph is another Issue. How ever assuming it is correct it shows that the red cells Have Minimum sensitivity at ~450nm and then sensitivity starts to increase towards 400.(Towards violet)

Which answers the question asked, Paraphrased as why do people seem to mix red to blue to make violet? Since the Red cells Sight amount of sensitivity in the blue regions, The colour Violet not only excites Blue but also the red cones. This receptivity is encoded in our perception of the colour Violet.

If the reader knows a more scientific resources where the sensitivity of Red cones can be obtained please post it in the comments section.

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That would be reflected in the retina wavelength sensitivity, which it isn't. So it's not a plausible explanation. – A.O.Tell Oct 14 '12 at 16:18
Do you have any evidence supporting it? – Prathyush Oct 14 '12 at 17:37
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sure: en.wikipedia.org/wiki/… – A.O.Tell Oct 14 '12 at 20:27
Take a look at en.wikipedia.org/wiki/Violet_%28color%29 "Spectral-violet looks like purple-violet for the human eye because L-cones have a secondary response in high-frequency blue" – Prathyush Oct 14 '12 at 21:02
@Tell that graph you pointed to appears to not contain all the details of scientific results, Perhaps someone must modify it in Wikipedia. – Prathyush Oct 14 '12 at 21:22
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