Web Safe Colors
You may have heard of Web Safe Colors, also referred to as the browser-safe palette, Netscape palette, 216 palette, Web palette, and/or 6x6x6 color cube. All these terms refer to a set of 216 colors that can be viewed by someone using a computer equipped with a 256 color (8-bit) video card. In case you are wondering why there are only 216 Web Safe Colors out of a possible 256, it is because the remaining 40 colors vary on Macs and PCs. By eliminating the 40 variable colors, the palette is optimized for cross-platform use.
Today, very few people have 8-bit video cards so, in our opinion (and the opinion of a number of graphics experts) there is little need to limit your color selection to Web Safe Colors, unless you are developing sites to be viewed with cell phones or PDAs.
If you choose to use Web Safe Colors, the palette is built into most professional Web design/development tools, including Photoshop, PhotoImpact, Paint Shop Pro, Illustrator, Freehand, Fireworks, Dreamweaver, and GoLive.