World knowledge influences how we perceive the world. This study shows that this influence is at least partly mediated by declarative memory. Dutch and German participants categorized hues from a yellow-to-orange continuum on stimuli that were prototypically orange or yellow and that were also associated with these color labels. Both groups gave more "yellow" responses if an ambiguous hue occurred on a prototypically yellow stimulus. The language groups were also tested on a stimulus (traffic light) that is associated with the label "orange" in Dutch and with the label "yellow" in German, even though the objective color is the same for both populations. Dutch observers categorized this stimulus as orange more often than German observers, in line with the assumption that declarative knowledge mediates the influence of world knowledge on color categorization. (Contains 3 figures and 1 footnote.)