Three chromatic reference stimuli (red, green, and blue) seen under five adaptation conditions (red, green, blue, achromatic, and darkness) were appearance-matched to subsequent color stimuli seen under achromatic conditions. The experimental results have been used to verify the opponent-color color-vision model and also to check the validity of some of the published transformation equations for predicting the tristimulus values of colors matched to a reference stimulus seen under different chromatic-adaptation conditions. It is concluded that the extant transformation laws are not sufficiently general to be applied to all adaptation conditions.