When specifying colors for Web page backgrounds, fonts, and other elements for 256-color displays (the most common display capability), you will probably want to choose from the 216 colors that look the same on both PC and Mac operating systems. Both the Netscape and Microsoft browsers have to work without the colors that each operating system reserves for itself. Since there are a total of 40 reserved colors on both systems, that leaves 216 colors for you to use. If you do use one of the 40 colors, each system tries to approximate it with some combination of the 216 acceptable colors (this is called dithering). Unfortunately, each operating system does dithering a bit differently. The result on a browser on one or both of the operating systems is likely to not be what you intended.