In five experiments, 10-month-olds were habituated to exemplars of a form category and tested for categorization in paired-comparison trials involving in-category versus out-of-category stimuli. Across these experiments, color was systematically manipulated during habituation and/or test trials. Infants categorized form when color was either held constant or varied during habituation, but failed to categorize form when exposed to color-constant stimuli during habituation and tested for categorization with novel-color form exemplars. Two subsequent experiments traced this failure to the narrow experience of exposure to color-constant exemplars during habituation. These results suggest that (a) infants' internal representation for a category will not include a stimulus dimension not varied in the exemplars from which the category was derived, but (b) if variation in that dimension is experienced, exemplars constructed of novel instances of that dimension will still be regarded as belonging to the category.