Cover picture: Among mammals, only primates have trichromatic color vision based on three spectral cone types: S-cones, M-cones, and L-cones. All other mammals have only S-cones and L-cones, and they are, therefore, dichromats. The cover picture shows the mosaic of S-cones (in green) and L-cones (in red) in the dorsal retina of the mouse. The retinal circuitry subserving color vision in nonprimate mammals is not yet known, and the article by Haverkamp et al. in this issue (pages 5438–5445) describes an S-coneselective bipolar cell of the mouse retina. This bipolar cell was labeled in a transgenic mouse line in which Clomeleon, a chloride-sensitive fluorescent protein, is expressed under the control of the thy1 promoter. The S-cone-selective circuits of the mouse and of the primate retina are very similar and represent the phylogenetically old color system common to all mammals.