I easily believe that in the USA all the people involved would be considered 'black'. That's understandable when looking at your history.

In the context of the country involved the people considered by themselves and by others as 'Arabs' are easily distinguishable (with few errors) from the others. How else would one party know whom to kill and whom not.

Musa Hilal (considered by most as the leader of the Janjaweed)
A Darfurian refugee

Wolfgang