The thing with half cast is that once again it is correct. You have a black father and a white mother and then you have a child that is a mixture of those genetic types. To be called half whatever is just a definition of how one appears. They are not James Toney black and they are not Hitler white, they are quite definitely something inbetween and I see nothing negative in being able to describe someone's appearance.

Half cast might have negative connotations because of history, but you would do just as well to have another word, perhaps 'halfcolour' or the more politically correct 'people of half colour'. Well, that just sounds stupid, just call them half casts and educate society to become more tolerant of ethnic diversity which in many ways the UK is. Certainly much more so than somewhere like Korea.