It does not help the cause of non-white British actors that when a plum star part in a British film comes up, it is likely to go to a name from America. Clearly, this is to do with raising finance. One example is Forest Whitaker as Idi Amin in The Last King of Scotland. Another is the choice of singer Jill Scott to shed her urban sophistication (and no doubt put on a few pounds, as Renée Zellweger does for Bridget Jones) to become the traditionally-built Mma Ramotswe in the No. 1 Ladies' Detective Agency series. All three actors were superb, but one felt that there were British or Commonwealth performers who could have filled the rôles.
I am not arguing for the sort of protectionism enforced by Actors Equity and the Musicians Union in the 1950s where there had to be an arithmetical balance between performers crossing the Atlantic. How pointless those restrictive practices were, was shown when they were lifted. What is more clearly needed is a more enlightened attitude on the part of writers, commissioners and casting directors in the UK.
A stray thought: it occurred to me when his name came up in Homeland: when in Hollywood, did David meet his near-namesake Dorian Harewood? It is not a common surname, so one suspects that though they are unlikely to be related they may have a dark common heritage in the identity of a seller of slaves in the southern States or the West Indies or both.