Im very much in the "not racist" camp on this one. I do not think that describing someone by their skin colour - or any other physical characteristic - should be considered offensive or racist. Effectively, by saying that one should not refer to a black person as black, you are implying that "black" is an offensive or derogatory term, or that it is something the person should be ashamed of or wouldnt want to hear. I do not believe this is or should be the case.
Secondly, on the point of people having a right to be offended by things. This is true, everyone has the right to be offended by whatever they like. However just because you are offended doesnt mean you are right. If I take offense at someone saying "hi" to me, then that doesnt automatically mean that word should be censored. Similarly, I do not believe that referring to someone by their skin colour is "reducing their identity to their colour" or any such arguments. It is simply a descriptive term - others may be available, but depending on the context, skin colour may simply be the most appropriate to use (as I believe was the case in this incident). Using black as a description in this way does not preclude the individual from having plenty of other characteristics and takes nothing away from their identity, it is simply one part of it.
Racism is vile and has no place in society. I define racism as the existence of prejudice or discrimination for or against people of a specific race. That has not happened here from what I can tell. There was no discrimination, no difference of treatment. Hell, the decision by the referee had already been made before he knew the identity of the "perpetrator".
Finally, if you introduce double standards - for whatever reason - in whether its ok to refer to a white person as white, vs a black person as black, you are on to a losing proposition. At some point you have to put the past in the past. None of the current generation were responsible for slavery, or events from hundreds of years ago, and similarly none of the current generation are direct victims of it. Racism absolutely still exists and needs to be stamped out, but constantly treading on egg shells due to the crimes of our ancestors is not the way to do it, for me.