A series of experiments are reported which use highly practiced subjects to investigate the effectiveness of color coding relative to letters, digits, and familiar geometric shapes. These experiments were concerned with unidimensional and bidimensional displays and relatively simple single tasks (choice reaction time, search and locate, and multiple target identification). The results are presented in a format which may be used as a practical guide for when and where to use color in displays. In addition several issues of more general theoretical interest are discussed. (Author)