PURPOSE: Recent theories of color-graphemic synesthesia posit that synesthetic color experiences arise from activation of some of the neural mechanisms involved in real color processing. But how early in color processing do synesthetic colors emerge? To investigate this question, we determined whether synesthetic colors are affected by brightness contrast. METHODS: Using a matching procedure, we obtained color appearance measurements from three color/orthographic synesthetes. Each participant carefully adjusted the hue, saturation and brightness of a 1-deg circular target situated on the right-half of a calibrated video monitor until it matched the color appearance of a small test figure appearing on the left-half of the monitor. In the synesthetic-color condition, the test figure was a fixed luminance (30cd/m2), achromatic alphabetic character that induced synesthetic color. This test figure was centered within an equal-energy-white (EEW), 3-deg circular background whose luminance varied from 10 to 30 cd/m2 over trials. The matching target adjusted by the observer also appeared within a 3-deg circular background whose EEW luminance (30 cd/m2) remained constant over trials. In the nonsynesthetic condition, the test figure was a real colored, non-alphabetic symbol that did not induce synesthesia; the symbol's chromaticity values corresponded to those estimated from the isomeric matching in which both backgrounds were 30 cd/m2. RESULTS AND DISCUSSION: In the nonsynesthetic condition, the matching luminance of the chromatic test symbols was inversely related to the background luminance against which those symbols were viewed; the colored symbols, in other words, were robustly susceptible to brightness contrast. In the synesthetic-color condition, however, the matching luminance of the synesthetic colors was invariant with background luminance; synesthetic colors, in other words, were immune to brightness contrast. Evidently, synesthetic color experiences emerge relatively late in the hierarchy of stages involved in color appearance.