Colors and the study of human experience
A satisfactory explanation of color perception has yet to be found relative to the known facts of retinal action and physical stimuli. Color may be defined as either an external stimulus or an internal perception. An individual's recognition and reaction to colors are determined not only by sensory stimulation, but also by the manner in which they are interpreted (Encyclopedia Americana, 1963, Vol. 22). Of course, one cannot deny the reality of "color experience," but color defined only, as "experience" is not susceptible to direct experimental measurement: the "experience" can only be inferred from stimulus or behavior.