This is part of the Human perception programmeBack
The colors perceived by humans in response to light stimuli are generally described in terms of four color categories (reds, greens, blues and yellows), the members of which are systematically arrayed around gray. This broadly accepted description of color sensation differs fundamentally from the light that induces it, which is neither ‘circular’ nor categorical.
What, then, accounts for these discrepancies between the structure of color experience and the physical reality that underlies it? We suggest that these differences are based on two related requirements for successful color vision:(1) that spectra be ordered according to their physical similarities and differences; and (2) that this ordering be constrained by the four-color map problem.
A rationale for the structure of color space.
Lotto, R.B. and Purves, D. (2002)
Trends in Neuroscience 25:82-86.