I've found that mozilla based browsers seem to handle CSS just fine when it's done properly, but that IE handles it well even when you've made mistakes in the coding.
Don't know if that's the case here or not, but I was very confused when I started doing this:
<img src="image.jpg" style="position=absolute;left=45;top=345"> and it worked fine in IE, but wouldn't work in firebird/netscape/mozilla, because i used an = instead of a :.
I've never tried using the RGB(r,g,b) before, but check your syntax to make sure it's 100% correct, by W3C standards. That may be the whole problem.