I think that any honest reader with minimal reading comprehension skills would realize the driving issue is the reason for the choice, not the actual choice. In your hypothetical case, if the reason was that black people are odious, then it is racial discrimination. If the reason is that the board needs some diversity for some reason, then no.
That may be a reason to call it 'justified racial discrimination' versus 'unjustified racial discrimination' but it's still discriminating by race if you're discriminating by race, no matter what your motives.
There are times when it's justified to discriminate by race (and gender, and other immutable characteristics). But I do not find 'diversity' to be a justifiable reason.