ARCHIVED: What are the 216 web browser-safe colors?

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On 8-bit displays (used with older computers), which only have memory for 256 or fewer colors, browsers such as Internet Explorer use a palette of 216 colors that is the same across platforms. The remaining 40 colors are different in Mac OS X and Windows, so if you use colors outside of these 216, they may be dithered or substituted on some older computers.

You can visualize the layout for the color palette as a three-dimensional grid, with its three axes corresponding to the RGB primary colors of red, green, and blue. Browser-safe colors are composed of any combination of the primaries in only these saturations: 0%, 20%, 40%, 60%, 80%, and 100%. The hexadecimal equivalents of these saturations are 00, 33, 66, 99, CC, and FF, respectively. In decimal, they are 0, 51, 102, 153, 204, and 255, respectively. Therefore, in an HTML tag with the BGCOLOR attribute, #CC00CC is browser safe, while #DD15C3 is not.

Many graphics programs give you the option of using the browser-safe palette for your images. In Mac OS X, the HTML Color Picker has this option built in. To get to it, in the Colors window, click Color Palettes; then, next to "List:", select Web Safe Colors.