Web Design in a Nutshell, 2nd Edition

Monitor Color Issues

Monitors also differ in the number of colors they are able to display, if they display colors at all. This is another aspect of the final display that may influence design decisions. Monitors typically display 24-bit color (approximately 17 million colors, also known as the “true color space”), 16-bit color (approximately 65,000 colors), or 8-bit color (256 colors). When colors taken from the “true” 24-bit color space are rendered in browsers on 8-bit monitors, many of the colors have to be approximated, and a speckled pattern (called dithering ) may occur.

However, there is a set of 216 colors, made up from the cross-section of the Windows and Macintosh system palettes, that will not dither on Windows and Mac 8-bit displays. This set of colors is known as the web palette, among other names. Many designers choose to design web graphics and HTML elements using colors from this palette so the pages look the same for all users. The web palette is discussed thoroughly in Chapter 3, Chapter 15, and Chapter 22.

If you are concerned about users with grayscale or black and white displays, be sure to design graphics with good contrast. When colors are converted to grayscale values (or dithered with black and white pixels), only the brightness of the colors matters. Imagine setting purple text on a teal background; although the colors are of contrasting hues, they are close enough in overall brightness that the text will be illegible when the colors are displayed ...