The effect of background color on chromatic adaptation and hence the appearance of object color is reviewed. The effect of lights at different wavelengths was assessed by observers who varied the intensities of two admixed lights to maintain a perceptual criterion, this being that the test color should appear neither reddish nor greenish. The findings are presented graphically and are related to the two-process theory of chromatic adaptation previously presented by Hurvich and Jameson (reference in article). Thus the adapting light alters the receptoral sensitivities while also contributing an additive element to the opponent chromatic responses.