Psychophysical evidence exists for three cones that each have absorbance peaks at
different areas of the visible spectrum corresponding to red, green and blue. The
trichromatic theory assumes that the differential input received from the three cone
systems serves as the basis for the colors we perceive (Matlin & Foley, 1997).
Trichromatic theory may be accurate in describing the beginning stages of the visual
transduction process, but it is not sufficient by itself to account for color perception. At
this point then, the opponent-processes theory of color vision takes us to the next level.