FIGURE 5.

Surface color perception under scotopic illumination reveals relational hue percepts mediated exclusively via the rod pathway. Symbols show the reported color names from four trichromatic observers of the gray OSA-UCS color sample as a function of photopic illuminance. Symbol size refers to the lightness of the OSA-UCS sample, with lightness increasing with increasing symbol size. Light levels below about -2.25 log Lux are solely mediated by rods; the colored shaded areas demarcate the blue–green–gray and red–orange color categories used by the observers (samples below threshold were black). Adapted from Pokorny et al. (2006).