With the introduction of low-cost color graphics systems comes a host of problems specifically concerned with the color aspect of the system. This paper discusses two of these problems: the selection and manipulation of colors by (possibly) inexperienced users, and the automatic selection of colors by the system to achieve high contrast effects on the screen. A new color space based on color opponency theory is described. This space is useful both in the user interface and in the automatic selection of high contrast colors.