Effect of black background on color appearance of NCS samples

Three samples, differing only by one step in blackness s and/or chroma c, were selected from each of 24 hue pages in the NCS atlas. Skilled NCS staff members compared two of the samples on differing (black or gray) backgrounds and later made absolute judgments in NCS notation for the same samples. Comparison judgments of relative lightness were closely correlated with judgments of relative whiteness/blackness. Samples received lower s notations when viewed on black backgrounds than when viewed on gray. Mean c notations were also lower on black than on gray for most samples. But values of chroma (C) computed according to the Hunt 94 color appearance model are consistently higher on black than on gray proximal fields. Lightness (J) values computed by the same model indicate, as expected, that the model fails to give a satisfactory account of simultaneous contrast.