Fig. 20 Confusion lines for colors used against a gray background in plate (#17) from a new version of a common book test (AOHRR) shown at bottom. Note the colors near the spectral locus (left side) for the confusion line that passes through gray (white) for protanopes (top) and deuteranopes (middle). They differ slightly, but enough to distinguish these dichromats from each other. With this plate in the actual book test (illustrated bottom) each sees only one of the two symbols. Reproduced with permission from Richmond Products Inc, Boca Raton, FL.