The relation between the r-g opponent-color transformation and the cone mechanisms was analyzed by determining the shift of unique yellow locus under chromatic adaptation and the t.v.i curves of the M and L cone mechanisms. The shift of unique yellow locus could not be accounted for by the model of Buchsbaum & Gottschalk (1983) and von Kries coefficient law. It is suggested that multiplicative adaptation mechanisms at post receptor process may contribute to the adaptation behavior of the r-g opponent-color system.