Chapter 4 – Color

Publisher Summary The purpose of this chapter is to develop a theory-based approach to how color should be used in design. There are two basic types of light receptors in the retina at the back of the eyeball: rods and cones. Rods, the most numerous type of light receptors, are specialized for very low light levels. Cone receptors are the basis for normal daytime vision, and they come in three subtypes—short-wavelength sensitive, middle-wavelength sensitive, and long-wavelength sensitive. Most of the important principles for effectively using color in design can be derived from an understanding of the red-green, yellow-blue, and black-white color channels. The most important single principle in the use of color is that whenever detailed information is to be shown, luminance contrast is necessary. However, it is also possible to get excellent luminance contrast with yellow on black or dark blue on white. As graphical features get larger, so the need for extreme luminance contrast declines. There are strict limits as to how many colors can be used effectively as codes. If a design is complex and the symbols are quite small, then no more than a dozen codes can be used with complete reliability. A particular specialized use of color is the color coding of maps. One kind of color sequence that is often used by scientists is an approximation to the spectrum of light.