Abstract: Identical colored paper chips were matched under various phases ofdaylight and another light source composed of RGB primaries. Spectrophoto-metric measurements were made of the two light sources, and the coloredchips under these conditions were computed for their chromaticities on theCIE 1931 color diagram. The matched colorimetric shift under the RGBprimaries was a measure of the degree of color constancy as perceived bythe observer. It was found that when matching single colors (Y, BG, P, YG, R) thecolorimetric shift was much less then that of computed physical colorimetricshift under changing natural daylight, which means that the perceived colordid not change in proportion with the spectral changes of daylight. In thisway it was possible to make objective colorimetric measurements of colorconstancy. The same phenomenon of breaking down of color constancy wasobserved with matching of colors in a meaningful picture. It seemed thatcolor constancy, like all other perceptual phenomena, has as its basis verycomplex physiological and psychological processes.

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