click image to enlarge the 216 color safe palette
There was a time when you could only use these colors on a web site--to ensure colors wouldn't dither (where a color is created by mixing dots, crosshatches, etc., of more than one color to create the illusion of another color). In 1996, most computers had 8-bit video cards (e.g, capable of displaying 256 colors).
The Browser-Safe Palette actually uses 216 colors (see swatches above) of the possible 256. The other 40 colors vary on Macs and PCs; not using those colors allows this palette to work cross-platform.
The woman who first identified the safe palette said:
"The browser-safe palette was developed by programmers with no design sense, I assure you. That's because a designer would have never picked these colors. Mostly, the palette contains far less light and dark colors than I wish it did, and is heavy on highly saturated colors and low on muted, tinted or toned colors. "