A structural comparison has been made of the tightness, chroma, and hue scales of the Munsell system, as expressed in the Munsell Renotations, and of rite OSA-UCS system. While the lightness scales are similar (except for the adjustment for the Helmholtz-Kohlrausch effect and the inclusion of a "crispening" effect in OSA-UCS), there are significant differences in the chroma scales along the major chromatic axes. Unlike in CIELAB, the increments in X and Z along these axes for equal chroma steps in both systems do not fall on a continuous function. In the two systems, as well as in CIELAB lines connecting colors of equal chroma differences at different Y values point to nonreal origins. These differ among the three systems. A major difference between Munsell and OSA-UCS is the size of the first chroma step away from gray. An experiment has been performed with the result that the OSA-UCS system is in lurch better agreement with the average observed in this respect than the Munsell system. OSA-UCS exhibits considerably more internal uniformity in terms of X and Z increments between steps than the Munsell system. (C) 2000 John Wiley & Sons, Inc.