A vector model for the simultaneous contrast of equiluminant colors is proposed. The main characteristics of simultaneous color contrast are associated with the interaction of the test and induction fields. The mechanisms of color contrast depend on the activity of neurons which subtract excitation arising in analogous neurons of the test and induction fields. Signals from the “subtractor” neurons pass via local inputs to “adder” neurons. Selective color detectors are excited by contributions from the adder neurons. When the induction and test fields are of identical color and their excitation vectors coincide, the color of the test field depends on neurons excited only in the test field, and the induction field has no effect on the color of the test field. When the test and induction fields are of different color tone or saturation, the color of the induction field affects the color of the test field such that the excitation vector of the test field diverges from the excitation vector of the induction field. This model can be used for analysis of neurophysiological and psychophysiological studies of color contrast.