The colours used in web pages (and images) are usually indicated using 3 pairs of hexadecimal values, in the order for Red, Green, Blue. Thus a background colour of red could be indicated by using the value "FF0000". That means full red, no green, no blue. The table below uses the values 00, 33, 66, 99, CC, FF to generate the colours. These colours are considered "web-safe" because most users can only display 256 colours on their computer. If you define a colour outside this range, it has to be made up of the existing colours either by a process called dithering, or by conversion.

If you can avoid either process, your images and colours will look better. A standard colour map using 6 variants of red, 6 variants of green, and 6 variants of blue results in 216 colours. If you use colours from this standard map, your pages and images will be more consistent when viewed with different browsers.