Six well-known color difference formulae CIEL*a* b*, CMC(l : c), BFD(l : c), CIE94, LCD and CIEDE2000 were investigated in this study with a series of visual color-difference data integrated from the experiments conducted under various conditions with changes in illumination and in separation between specimens made of woolen serge. The results indicated that the separation between specimens had a significant effect, with the largest decreasing percentage about 44 % among those for all the experimental conditions used on the magnitude of visual color difference for the pairs of specimens having the color difference larger than three CIEL*a* b* units as juxtaposed. Furthermore, the larger the separation between specimens, the worse the performance of all the color difference formulae tested in estimating visual color differences was, with the exception of those originally visual matching each other under a specific light source. In addition, the color difference formula CIE94 had the best total performance in predicting the visual color difference under all three light sources D(65), A and OFF, as well as the conditions of the separation between the specimens used, while the CIEDE2000 and CIEL*a* b* had the worst.
