Achromatic loci in normal and anomalous trichromats.

The stimuli that appear achromatic anchor color space and exhibit multiple properties that reflect an alignment of color vision with spectral characteristics of the chromatic environment. We examined how well this alignment is preserved in individuals with anomalous trichromacy. Observers viewed stimuli spanning a range of chromaticities and luminance contrasts relative to a nominal gray background of varying luminance, and classified the stimuli as achromatic (white or gray) or chromatic (one of eight color terms). For color-normal observers, the achromatic categories were constrained in size and tended to vary along a blue-yellow axis, with a bias toward blue. Anomalous observers had larger achromatic regions and less evidence for a blue-yellow orientation. However, the range of stimuli labeled as achromatic was often substantially smaller than the range predicted by their threshold sensitivity losses. This discrepancy is consistent with partial compensation of color perception or color naming for the altered spectral sensitivities of anomalous trichromats.