Do you know that man, the black one?

A couple of times in the last weeks friends have used this approach to try to describe someone to us. Of course we find it incredibly funny and a very ineffective way of identifying someone. There are undoubtedly very different shades of skin colour, so "black" is used as opposed to brown, not white. It is also quite possible to identify different ethnic groups (I'm not referring to H and T in Rwanda, but "Congolese", "Munyamulange", "Twa", etc.). However, it still seems a strange starting point as a description of an inhabitant of Central Africa.