This would require many, many decals.
Even more than we have now.
For every decal we have, we need 15 more decals for each one.
You can see the problems this would present.
Not to mention that this kind of script would be similar to having the "Rainbow_Player" script, which changes body part colors. This works on a similar principle.
It would, indeed, provide a bit more atmosphere, however, it would increase download times and require thousands of lines of code.