I recently went through my CSS file and switch all my 6-digit hexadecimal codes to simple 3-digit codes (for example, my
The 3-digit codes are shorthand,
#123 is the same as
#112233. In the example you give, you've (effectively) swapped
#FFFFFF, which is close to the original colour but obviously not exact.
It doesn't "matter" which version you use, as such, but 3-digit colour codes mean you have a little less choice in shades. If you feel that saving 300 bytes is worth that, then go ahead and use the 3-digit codes, but unless you're designing for a low-bandwidth situation those 300 bytes won't really save you all that much.