We may be able to attribute much of the interest and research produced in the area
of color vision to the debate between supporters of three color vision theories. The
trichromatic theory and the opponent-processes theory of color vision are cognitive in
nature (Hering, 1961), while Retinex theory (Land, 1977) is computational (Livingstone
& Hubel, 1984) .
The Young-Helmholtz trichromatic theory states that the retina has three types of
color receptors, each differentially sensitive to red, green and blue. Each receptor may be
stimulated at any wavelength but maximally responds to the wavelength to which it is
most sensitive (Goldstein, 1999).