Most studies of surface color appearance have ignored 3-D illumination phenomena such as shadows and interreflections, These phenomena must affect surface color appearance to some extent, but without a model we cannot make claims about how great these effects really are. In this article, we introduce a simple model of how interreflections car? affect color appearance. We consider a family of ideal surfaces, namely spherical concavities dug out of a ground plane, and we assume that these surfaces are illuminated by a uniform, diffuse light source. Under such assumptions, the color signal reflected from a surface is described by a simple mathematical model. We use this model and CIELAB coordinates to perform a parametric study of how the lightness, hue, and chroma of the reflected color signal vary with the concavity aperture. We find that interreflections can significantly affect color appearance of spherical concavities, but only if the surface has high lightness. (C) 2000 John Wiley & Sons, Inc.