Color constancy in natural scenes independent of an explicit illuminant cue

The ability of observers to make reliable judgments of surface color despite changes in an illuminant ("color constancy") has sometimes been attributed to their estimating the spectral properties of the illuminant in order to discount its effects. To test how information about the illuminant contributes to surface-color judgments, observers' performance in two surface-color-matching experiments with natural scenes, acquired with a high-resolution hyperspectral imaging system, was subjected to a multivariate analysis of variance. In the first experiment, the sky was directly visible to the observer, and its color was varied. In the second experiment, a large gray sphere was introduced into the scene so that its illumination by the sun and sky was directly visible to the observer and the color of that illumination was varied. Although observers' surface-color matches varied across conditions, there was no reliable effect of the illuminant cue. Even when the sky was invisible, performance did not worsen. Judging surface color in natural scenes seems not to require knowledge of the illuminant.