Web Design in a Nutshell, 3rd Edition

Color Depth

The number of colors from the RGB color space a monitor can display at one time is known as its color depth. More specifically, color depth is the number of bits of data used to represent the color of a single pixel on the screen (also called bits per pixel or bpp).

The vast majority of monitors fall into one of three color depth categories: Truecolor (millions of colors), Highcolor (also called HiColor; thousands of colors), or Indexed color (256 colors or fewer). How these systems work has a direct impact on the quality of your colors and tasks such as matching colors in graphics and backgrounds.