Why do we recognize uniqueness only for four colors, blue, yellow, green, and red? Is there any color map of unique hues in a visual system?
There seems to be a lot of physiological and psychophysical evidence supporting the special nature of the unique hues in the human visual system. I’d suggest a google scholar search to find lots of interesting references. “Why” is a difficult question, but it is probably related to the nature of the cone photopigment absorptivities and the transformation of them necessarily to maximally decorrelate the spectral signals in the natural world. It is hard to say there is an exact physiological locus for the unique hues, but there are certainly various types of opponent encodings that have been identified and there is certainly a map somewhere in the visual system because the response is such an easily accessible percept.
