Deciding how to use color in computer applications is a very difficult problem. Some of the difficulty resides in the characterizing the output medium. Color production systems vary in their underlying color models, their intrinsic color gamuts, and even the angular distribution of the light stimulus reaching the human observer. Some of the difficulty resides in understanding the human perceptual system which is receiving this input. Perhaps most elusive of the difficulties, however, is how the interaction between the physical stimulus and the observer depends on the task the user is trying to perform.