Of the standard 256-color VGA palette, Web browsers can accurately display only 216 colorswithout dithering (approximating the specified color using pixels in colors that the computer candisplay). Here is a table showing those colors, with the appropriate RRGGBB designations. The216 non-dithering colors are in the center; the side columns are for reference.
Yes, I freely ripped this off from the web.. see credit at bottom!
Thanks to Doug Jacobson for the color chart.