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Appendix E: Color Reference

This appendix provides basic information about the use of colors on the Web, from how to calculate browser-safe colors, adjust unsafe colors, and form hybrid colors, to the use of color names and their numerical equivalents as used in HTML and CSS, and browser support of color names.

Browser-Safe Colors

While 8-bit GIF images support 256 colors, cross-platform issues leave a palette of only 216 colors that are completely safe to use on the Web. This group of Web-safe colors is often called the browser-safe palette. Since it is difficult to present this information visually in a black and white book, the palette can be viewed online at http://wwwlref.com/reference/AppE. Use of other colors beyond this safe set can lead to poor-looking images when viewed under limited color conditions such as 8-bit (256 color) VGA. Selecting a set of colors from the safe color palette and mixing them together in a process called dithering will approximate colors outside the safe range. In short, dithering attempts to imitate colors by placing similar colors near them, but generally creates irregularities that render the image unappealing.

The selection of the 216 safe colors is fairly obvious if you consider the additive nature of RGB color. Consider a color to be made up of varying amounts of red, green, or blue that could be set by adjusting an imaginary color dial from the extremes of no color to maximum color saturation. The safe colors use six possible intensity settings for each value of red, green, or blue. The settings are 0%, 20%, 40%, 60%, 80%, and 100%. A value of 0%, 0%, 0% on the imaginary color dial would be equivalent to black. A value of 100%, 100%, 100% would indicate pure white, while a value of 100%, 0%, 0% is pure red, and so on. The safe colors are those that have an RGB value set only at one of the safe intensity settings. The hex conversions for saturation are shown in Table E-1.

Setting a safe color is simply a matter of selecting a combination of safe hex values. In this case, #9966FF is a safe hex color; #9370DB is not. Most Web design tools like Macromedia Dreamweaver contain safe color pickers as do imaging tools like Macromedia Fireworks or Adobe PhotoShop. Designers looking for color palettes, including improved color pickers and swatches, should visit http://www.visibone.com/colorlab/.

Setting an unsafe color to its nearest safe color is fairly easy-just round each particular red, green, or blue value up or down to the nearest safe value. A complete conversion of hex to decimal values is shown in Table E-2. Safe values are indicated in bold.

Although mathematically translating to the closest browser-safe color seems appropriate, it might not look correct to many people. Consider creating a hybrid color by combining multiple safe colors together. This is done simply by creating a checkerboard effect with a GIF image, in which two or more non-dithering colors are placed side by side to give the appearance of a third color. A variety of PhotoShop plug-ins such as Colorsafe (www.boxtopsoft.com) exist for mixing colors.