And, pen, even IF the face-blacking in question is 'about' black people (in the sense of saying this sort of dance originated in Africa, which I don't think anyone knows for sure, but it's possible, obviously) what is there to get upset about? It's not in a way that is unpleasant or in any way derogatory.
What would people say to a group of Britons, having spent months or years learning about and practising, say, Maori dances, or Thai dances, or whatever, who then dressed up in the kind of way Maoris or Thais or whatevers did when dancing, and performed the dances for the entertainment of other random Britons? Would it be wrong? I don't think it would be any wronger than learning a foreign language and speaking it.
I did try Thai dancing. It's bloody difficult. Also Spanish. Ditto re difficulty. Also Scottish. I was good at that. I'm not Scottish.
All very silly, as I said.