Web-safe colors
From The Glossary of Digital Photography
Also called web colors. A group of 216 colors that will display uniformly in most computers and web browsers. In addition to the 216 colors, there are forty additional colors that are unique and reserved for the use of various operating systems. At one time computers could only display 256 colors, so the web-safe colors were configured so they would work on these earlier computers. Many monitors and computers can display more colors because they have moved from 8-bit to 16- and 24-bit displays. This has caused the use of web-safe colors to decline.
