I normally try and answer questions in an in-depth manner but there is just not alot to say on this matter. Does "black" mean south-African descent? Does "black" mean Dravidian people from south India? In both cases the easy answer is "no" because they did not live near the (current) Nepal/India border where Siddhartha Gautama is said have been raised and born.

Dr Umar Johnson claims that Buddha was black and his main reason for thinking this was early statues of Buddha

For almost 300-500 years after the death of the Buddha there was a strong rule in Buddhism to not represent the Buddha in statute format. So when the Greeks eventually ended up influencing the Buddha in statue format, it had been a very long time after living memory of what he actually looked like. Its not a very astute or educated opinion he has.