Deuteranomalous trichromacy is the most common form of inherited color-vision deficiency. A modern description of its cause is a single abnormality: the normal middle-wave cone photopigment (M) is replaced by a shifted middle-wave pigment (M′) that is shared by all deuteranomalous trichromats. This explanation, however, fails to account for the individual differences in color vision observed even within the sub-group of deuteranomals with good chromatic discrimination. An ensemble of color matches is used here to test whether these individual differences reflect differences in the wavelength of peak sensitivity (λ max) of individual deuteranomals' cone photopigments. The results show variation in both the λ max and the effective optical density of their cone pigments. The individual differences found in λ max are in accord with recent molecular biological research that shows individual differences in the genes thought to encode deuteranomalous photopigments. © 1997 Elsevier Science Ltd. All rights reserved.