Sir: David Lister surely confuses the point about black/white casting. When a play or film is about characters whose race is specified and where race is central to the theme, the race of the actor is relevant. But in most cases race is not relevant and there is no reason why a black actor should not play the part of Henry IV or Jimmy Porter.
Drama invites its audience to suspend disbelief. The race of the actors is only a factor in a racist society. Ira Aldridge was a celebrated African American who was renowned throughout the world as a Shakespearian actor.