ABSTRACT
The merit of the three-receptor model went far beyond explaining the laws of color mixing. One of its major successes was the explanation of various forms of color blindness, in terms of a reduction of normal trichromacy. If one of the receptor types is absent color space should collapse from three to two dimensional. Instead of Hermann von Helmholtz’ three-receptor model (red/green/blue), E. Hering devised his four-color opponent system: red/green and yellow/blue, combined with one achromatic balance, black versus white. This model indeed provides a basis for describing color appearance, though one should be a bit careful to use the term “model” for this more descriptive than mechanistic representation. There is probably no field of sensory modeling that has such a long and distinguished history as that of color vision. So long, as the first thoughts of a model seem to have emerged in the middle of the 18th century, some 250 years ago.
