A moving border formed by color contrast across which brightness contrast can be independently controlled was used to examine responses of ganglion cells in monkey retina. We used two forms of color contrasts, white/yellow and red/green. Three classes of ganglion cells were examined: blue/yellow opponent, red/green opponent and non-color opponent on-center phasic cells. Blue/yellow opponent cells respond strongly to white/yellow contrast at all brightness gradients, responding better to a white/yellow border at minimum brightness contrast than to a white/black border at maximum brightness contrast. These cells respond before and reach their maximum response long after the border has crossed the receptive field center. Red/green opponent and phasic non-opponent cells do not detect white/yellow borders at minimum brightness contrast; at sufficient brightness contrast phasic and some red/green opponent cells detect this border responding maximally as the border crosses their receptive field center. Red/green opponent and non-opponent phasic on-center cells respond to red/green contrast at both maximum and minimum brightness contrast. The former are excited by only one side, the latter by either side of the red/green contrast entering their receptive field. Phasic on-center cells have a maintained excitatory rod signal which is suppressed when a detectable border enters their field. The results suggest that the blue/yellow opponent system plays a major role in distinguishing white/yellow borders and has a poorer spatial resolution than the red/green one, that phasic ganglion cells receive a rod and a red/green but not a blue/yellow opponent input, and that this blue/yellow system has a retinal pathway which does not obviously influence rods or other cones.