Differential color thresholds from metameric matches: experimental results concerning failures of colorimetric additivity.

The differential chromaticity thresholds obtained by varying degrees of metamerism have been evaluated for five target chromaticities. Differences have been found between the chromaticities predicted by the CIE-1931 standard observer and those actually observed under our experimental conditions, with foveal fields of 3 degrees, luminance within the low photopic level, and sets of primary colors produced by filters of differing spectral bandwidths. Failures of colorimetric additivity under these experimental conditions are discussed. The results have also been analyzed by using other sets of color-matching functions, i.e., Judd's proposed modification at short wavelengths and also the supplementary standard observer, CIE-1964.