The color vision of five saddle-backed tamarins (Saguinus fuscicollis) was studied. Behavioral tests of color discrimination and spectral sensitivity indicate that this species has a color vision polymorphism. Individual monkeys have either dichromatic or trichromatic color vision. Measurements of the spectral sensitivity of cones on this species were made on nine animals with the technique of electroretinogram (ERG) flicker photometry. Both the electrophysiological and the behavioral results suggest that there are four classes of cone pigment in this species. In addition to a short wavelength sensitive cone, apparently common to all tamarins, there are three classes of middle to long wavelength cone (lambda max = 545, 557 and 562 nm). Individual animals have either one or two of the latter types. The color vision variation in this species differs for males and females.