A number of widely used color-difference formulae were compared using a set of nine reference colors distributed through color space. Five color difference vectors were defined for each of the reference colors. Tolerances were calculated for a standard D65 illuminant from the results obtained from 50 observers. Statistical analysis of the performance of color difference metric applied to the 45 color difference vectors studied indicated that weighted CIELAB color difference formulas, most notably the CMC, Colour Measurement Committee (of the Society of Dyers and Colourists) performed markedly better than the standard CIE color-difference metric. The best performance was afforded by regressional analysis carried out by the authors. This analysis, as they point out, only holds for the nine colors selected for this experiment and is not a generally applicable color difference metric.