A generic model of color discrimination is presented. Ir involves adaptive nonlinearities at photoreceptor level and in color-opponent pathways. This model, with few parameters, can reproduce the various aspects of the observed data from six individual observers, as reported in studies by MacAdam, Wyszecki and Fielder, and Brown and MacAdam. It is base on two main hypotheses: (1) all the observers have the same kind of nonlinear adaptive funct ions; (2) each observer has his or her own coding of color oppositions. Therefore, for each observer, the mean model parameters are adjusted to fit all the data in the particular available experimental conditions. The model is unique, one set of its parameters depends only on the adaptation state, the other set depends only on observer's specific color coding. We conclude that the observed variability in color discrimination data stem only: (1) from both difference in adaptation stares, due to experimental conditions; (2) from inter-observers color coding differences. (C) 2000 John Wiley & Sons, Inc.