Were it not for an algorithm patch, the color-appearance model CIECAM02 would sometimes be forced to evaluate fractional powers of negative numbers. The artifact arises because the red and green primaries of the initial CAT02 chromatic adaptation lie outside the positive gamut of the Hunt-Pointer-Estevez (HPE) primaries that subsequently convey the color signal in the model. Relocating the chromaticities of the HPE red and green primaries so as to lie on the CAT02 red-green line alleviates the problem, but adds a bit of X and Y to the revised HPE blue. An (x,y) diagram aids in visualizing the CIECAM02 gamut overlaps, with an extension that accommodates the HPE RGB triangle's enclosure of the point at infinity. (c) 2006 Wiley Periodicals, Inc.