We have examined how color appearance varies with spatial pattern. Subjects set color-matches between a uniform, 2 deg matching field and bars within squarewave patterns (1, 2 and 4 c/deg) or the superposition of these squarewaves. The matches were set using squarewaves and squarewave mixtures with many different colors and contrasts.
The color-matches satisfied the basic properties of a linear system to within a tolerance of twice the precision of repeated matches. Matches satisfied contrast-homogeneity: the contrast of the matching field was proportional to the contrast of the squarewave pattern or the mixture of squarewave patterns. Matches also satisfied pattern-superposition: if a bar in one squarewave matched one uniform field, and a bar in a second squarewave matched a second uniform field, the superposition of the two squarewave bars matched the superposition of the uniform matching fields.