Unique hue loci and implications

Abstract Unique hue loci of red, yellow, green, and blue were obtained for lights of 0.5 and 2 cd. m ‐2 from five normal color vision subjects. Most loci curved on the chromaticity diagram. This result excludes linear equations of colormatching functions as candidates for spectral sensitivity functions of opponent color systems, (r/g)λ and (y/b)λ. The chromatic valence curves of two opponent color systems obtained by the so‐called cancellation experiment were analyzed in relation to the unique hue loci and it was shown that the appearance of the valence curves can be manipulated at will by choosing the cancellation light at various points on the chromaticity diagram. A similar manipulation was also demonstrated for the additivity property of chromatic valence and it was made clear that no unique solution is obtainable.