When information is presented on a computer display in support of the human decision maker, but the amount of information is in direct proportion to computer processing powers, the human can quickly be overloaded. Because of its ability to attract and direct attention, color is one of the techniques used to enhance information display. However, the general rule that color is good for a search task, but not for strictly an identification task is limited in its applicability to complex displays: Certain design tradeoffs have to be made. Further, whether color is reported to benefit performance depends on the measure. The experiment reported here was a test of the effectiveness of color in simplifying coding, adding highlighting, and reducing clutter on an actual display, the display used in the US Army's Patriot high altitude air defense weapon system. Trained operators were tested with the existing monochrome display and an experimental color display, which was developed based on guidelines derived from the literature and on knowledge of the human/computer interface, including the operators' conceptual organization, or mental model, of the displayed information. Contrary to expectation, there was no general enhancement due to color with any of the measures taken, including the stated preference of the operators. Looking at the pattern of results over time, however, the trend was in the direction of an enhancement with color, specifically as measured by the timeliness of the engagement decision, by the pattern of activities showing the ability to use step-saving features of the system, and by subjective workload assessment. The lack of more immediate and widespread color benefits can be attributed to having to learn the color-category relationships even though early perceptual processing of color information is effortless, and to the inherent difficulty in designing a structured display to fit an unstructured task.