Behavioral discrimination tests were used to examine spectral sensitivity and color vision in a pair of ring-tailed lemurs (Lemur catta). Sensitivity tests revealed the presence of a Purkinje shift and a photopic visual system. As measured at increment-threshold, the photopic spectral sensitivity function for the lemur has multiple peaks (at ca. 440–460, 540, and 620 nm). In color vision tests lemurs behave trichromatically in that (a) they show no evidence for a neutral point in the spectral range of 470–510 nm, and (b) they set a unique Rayleigh match (540 nm + 645 nm = 570 nm). Tests of wavelength and colorimetric purity discrimination reveal that although this prosimian has color vision, it is not an acute capacity – thresholds for these color discriminations were consistently much higher for lemurs than for normal human trichromats tested in the same situ