In order to understand the representation of color it is necessary to consider three items:
Little attention has been given to the first item in this list, although it is this item which can be altered in order to best understand the other two items. Color researchers have taken the organization of the photic representational space as a given, when it is only the organization which simplified the problems which physicists needed to solve so as to understand the nature of electromagnetic radiation.
Psychophysical researchers have the opportunity to represent the space of photic stimuli in a variety of ways as long as these representations do not conflict with those of physical laws. A representation which would help understand the process of color vision is one which would remove the many--to--one nature of the perceptual mapping implied by color constancy. It is evident that at least general illuminance, local contrast and spatial frequency play a part in the process of maintaining color constancy. For this reason, it will be necessary to include objective measures of these qualities into the representation of the photic environment if a continuous function mapping visual stimuli onto color representation is to be found.
Perceptual color space has, until recently, been assumed to be three dimensional since only three types of color sensitive receptors exist on the retina. However, it has been demonstrated that three dimensions are insufficient to accurately reproduce and discriminate color spectral distributions reflected from everyday objects. Nonlinearities and spatial organization in neural codings of signals from the three types of retinal cones can potentially generate a representation which has a dimension greater than three; a four or five dimensional perceptual color space is not out of the question.
Systematic study of higher dimensional representations of the photic environment space and their attendant representations in perceptual color space is likely to lead to the discovery of the optimum dimensionality and metric for these two spaces which produce a visual perceptual mapping function that is both continuous and differentiable.