I was not into hip hop much around 6 years ago, only ever heard the mainstream artists but Eminem stood out clear to me cause at the time he seemed so clear with his words and something about Forgot About Dre stood out to me .. I guess it was timing as I was just turning into a team and the whole 'I don't give a fuck' vibe seems mighty cool at the time

.. now it does seem a tad immature cause wether or not you give a fuck, we live in a society ( well I do at least =D ) .. we're not giving a fuck and being a rebel won't get you anywhere.
So to answer the question, I don't think his skin colour has anything to do with it, I'd agree with others by sayng it was his style and timing that made things work.