Never Rely on Color Alone

Color coding should be limited to the emphasis of visual information conveyed by other means. Information should be carried, primarily, by font, text shape, layout, and the text itself. As outlined in some of the other principles of this section, there are many differences among individual perceptions of color, both physically (e.g., degrees of color blindness) and psychologically (e.g., in color connotations). An old designer's trick is to convert doubtful designs to monochrome (say by printing on a black & white printer), and then see how much information has been lost.