Even in this day and age, there are still people that are limited to 256 colors because of the video card/drivers on their older computers. So when designing a webpage, if you want to be considerate of those people, you have to think "browser-safe" when it comes to colors you pick out for your page. This little handy website called Colormix helps you by using dithering (which CAN be ugly if done wrong) the colors you pick by intelligently incorporating web-safe colors together to create a similar color to your liking and then creating a .gif swatch for you to download.