Here me out. Im only trying to help. I have no interest in the white 3Gs, but for those who do, check out the slider case made by incase. I had it for my 1st Gen and its the best case you can buy in my opinion and many others opinions.
I havent seen it yet for the 3G. They have the Protective case but not the slider. Anyway, they make them in white and it went get dirty nearly as fast as the stock shell of a 3G. Plus if it does, you remove it, clean it, replace it.
Im sure the Protective case is great too, but it has a pattern to it rather than a smooth finish. The slider was awesome because it had a piano black glossy surface, like the back of the 3G. Im tellin you, keep an eye out for the new slider if they make them. You wont be disappointed.