Berlin & Kay hue-related basic color categories are compared with the ISCC-NBS system of object color categorization. Though independently derived, categories of the former form a small subset of the latter. A conjecture is proposed that explains the absence of yellow-green and blue-green basic hue categories and the potential for a violet category as the result of constraints on primitive hue category formation due to considerable variation in stimuli selected by color-normal observers as representing for them unique hues.