Color appearance with sparse chromatic context.

We compared changes in the appearance of a test region caused by introducing an inhomogeneous chromatic background to changes caused by a space-averaged equivalent uniform background. Subjects adjusted a test field presented on a CRT so that it appeared neither reddish nor greenish. Sparse "white" or "green" dots, randomly scattered throughout a "red" background field, caused a large decrease (up to 15 nm) in the dominant wavelength of the red/green equilibrium setting, compared to measurements with a uniform "red" background. A uniform background with the same space-averaged chromaticity and luminance as the complex background had an effect similar to the uniform "red" background. These results contradict theories of color constancy that rely on the "gray world" assumption, and indicate the significance for color perception of individual chromaticities within discrete, noncontiguous regions.