A successive, asymmetric color-matching paradigm was used to investigate the link between cone contrast and the stability of perceived colors. We measured the perceived color shifts of 10 Munsell samples, induced by test illuminant A, simulated in u′v′ color space. The capacity of the visual system to resist these shifts, otherwise known as color constancy, is measured in terms of the Brunswik ratio, BR. Cone contrasts are calculated with respect to either the physical or perceived background. Subjective cone contrasts show a better fit to the von Kries law than those based on the physical background. Complete cone adaptation occurs when color constancy is high. However we show conditions where cone adaptation seems complete but color constancy is poor.

Human color vision is based fundamentally on three separate cone photopigments. Hereditary color deficiency, which affects up to 10% of males, results from an absorption shift or lack of L or M cone phototoreceptors. While hereditary S cone deficiency is rare, decreased S cone sensitivity occurs early in eye disease, underscoring the importance of quantifying S cone function. Our purpose is to describe a novel approach for quantifying human color vision based on the photopigments of normal color vision. Colored letters, visible to a single cone type, are presented in graded steps of cone contrast to determine the threshold for letter recognition. This approach quantifies normal color vision, indicates type and severity of hereditary deficiency, and reveals sensitivity decrements in various diseases.