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In the present study, we investigated the role of phenomenologically perceivedcolor differences between stimuli in determining visual search efficiency. Wecontrasted this with predictions based on the categorical color status, asproposed by Wolfe's Guided Search 2 model. We first asked participantsto rate the color similarity of each pair of stimuli (pairwise comparison). Theresults were combined using multidimensional scaling to produce a similaritymetric, which was subsequently used to define stimulus similarities for twovisual search experiments. The results demonstrate that the time required byparticipants to find a target is more adequately explained by the perceivedsimilarity of colors than by color categories.