Colour is a basic feature only if colour set is small (<~9) and colours are dissimilar Prototype colours are easier to find among non-prototype distractors - red target in magenta distractors. (see slide) So Wolfe?s Guided Search Theory: Attention needed to identify targets Preattentive basic features, e.g., colour can be used to guide search For feature search (e.g., ?red?) attention is directed