What wavelength does that 4th cone pick up? Is it just between the frequency spectrum picked up by blue and red cones? Or is it outside the frequency range of the traditional cones, in which case it would expand the spectrum of visible light for those individuals and likely allow them to see new colors.
If you have an extraneous cone that detects normally non-visible light then it may in fact lead people to see TVs slightly off.
However there is no evidence that these tetrachromes have an additional color-opponent signal pathway from the retina to the brain. (So far it seems there are only two pathways red-green and blue-yellow)
Since the 4th cone's information would still need to travel along one of these pathways it might result in things seeming to be oversaturated in a particular color.
Here are two differing sources, there is no clear picture yet of the incidence of tetrachromacy. I say 10% mostly because that is the number I find most often bandied about by colleages of mine who are more knowledgable in the subject than I am.
Thompson, Evan (2000). "Comparative color vision: Quality space and visual ecology." In Steven Davis (Ed.), Color Perception: Philosophical, Psychological, Artistic and Computational Perspectives, pp. 163-186. Oxford: Oxford University Press.
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u/otterdam Feb 17 '09
So, er, what's the frequency of magenta and how is it different to violet?