Evidence is presented that colar constancy does not exist as a special phenomenon of human color vision. It is argued that results of experiments, as well as casual observations, which seem to illustrate color constancy, can be easily understood from basic facts about chromatic adaptation and simultaneous contrast. The argument is supported by (i) a critique of the famous Mondrian studies, (ii) the ATD model's predictions of the Mondrian data, and (iii) a summary of a demonstration experiment regarding Mondrian patterns. Concerning definitions of color concepts, it is noted that, in any field of science, definitions change according to theoretical advances, but the vocabulary of color vision has not. In particular, the ATD models of the past ten years or so suggest that some of the universally accepted and seemingly essential terms of color require re-examination.