In the course of human and pre-human evolution, our eyes and brain have developed elaborate mechanisms for detecting and discriminating objects, materials, and living entities in our environment on the basis of their surface properties (e.g., slippery floor, red fur). One of the most salient properties that we use to identify objects in our environment is their perceived color. It is well known that surface colors are computed by the visual system from an analysis of the wavelength composition of the light reflected to the eye from the surface. It is perhaps less well known that the color appearance of objects remains remarkably stable under the challenge of changes in the overall environmental illumination or in the wavelength composition of the illumination: a phenomenon known as color constancy. Nevertheless, human color constancy is not perfect. A textbook demonstration, familiar to many students of Psychology, reveals that a gray paper viewed against a yellow background looks bluer than an identical gray paper viewed against a blue background. Thus, the color of a surface may be influenced by the spatial context in which it is viewed. I will describe research carried out in my lab on the effects of spatial context on the perception of achromatic colors: i.e., perceived shades of gray. Achromatic color perception is chosen as a simple model system for understanding the influence of spatial context on color perception, more generally. I will show how we have used data from perceptual experiments to construct quantitative and computational models of the effects of spatial context on achromatic color, and to probe the neural mechanisms underlying the visual computation of color. The quantitative models that we have developed both extend classical psychophysical laws relating perceived brightness to physical intensity and help to place those laws in an ecologically valid context. The computational models make contact with data from cortical single-cell recording studies and thus provide a theoretical link between the goals of color perception, its systems-level computations, and the physiological mechanisms used to carry out those computations.