ABNORMAL HUE ANGLE CHANGE OF THE GEMSTONE TANZANITE BETWEEN CIE ILLUMINANT-D65 AND ILLUMINANT-A IN CIELAB COLOR SPACE

The blue-to-purple color appearance change observed in some rare speci mens of the gemstone tanzanite between daylight and incandescent light is contrary to the hue-angle change calculated between CIE illuminant s D65 and A in CIELAB color space. This abnormal calculated hue-angle change for tanzanite can be corrected by using the spectral sensitivit y functions of the three kinds of cone photoreceptors to directly calc ulate color. This study suggests that the cone spectral sensitivity fu nctions are more fundamental in color calculations than the CIE color- matching functions. (C) 1995 John Wiley and Sons, Inc.