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.