"But who would you get for the movie?"
I seriously thought of D at least two shades darker: more like Denzel Washington, honestly.
But for the Bokor you need somebody darker than Idris Elba's (now-graying) beard, if possible. Realistically, Omar Epps is about as pale as I'd cast him. Adewale Akinnuoye-Agbaje looks like a better choice, despite not being quite so thin.