Color-vision variations represented in an individual-difference vector chart

The aim was to reconstruct a uniform color space that could accommodate normal and abnormal variations in color vision. Color-dissimilarity data were collected from normal trichromats and red-green deficients, using lights varying in spectral composition and luminance. The data were analyzed with an individual-differences multidimensional scaling program and resulted in a 3D group configuration. In addition, differences in saturation required a hemispherical representation for the “color plane,” with a 4th dimension obtained when a constraint of sphericity was included in the algorithm. Subject-specific color spaces were derived from this group configuration by axial compression, preceded by a rotation of the chromatic plane. In the spaces of color deficients, compression along a red-green axis occurred, though the direction of the compression differed for protans and deutans. The extent of the compression reflected the severity of abnormality. Transformations of the subject-specific color spaces — compression extent and the angle of rotation — were portrayed in a polar-coordinate chart. The chart separates normal trichromats from the red-green deficients, distinguishes protans from deutans, and quantifies the deficiency within each class.