Categorical perception (CP) occurs when discrimination of items that cross category boundaries is faster or more accurate than discrimination of exemplars from the same category. Categorical perception of color is observed when, for example, a green stimulus and a blue stimulus are more easily distinguished than two stimuli from the same color category (e.g., two different shades of green). Color differences in terms of discriminability can be equated across between-category and within-category comparisons by using the Commision Internationale de L’Eclairage (CIE) values. It is therefore important to note that superior cross-category relative to within-category discrimination is observed when the physical distance between cross-category items and the physical distance between within-category items are equivalent.