I mean, it's well-documented that there was intermarriage and trade with Kush, a land that covers Ethiopia, Sudan, and some other places south of Egypt with varying levels of melanin if that is how you are defining black. It's probably better to argue that Egypt's rootstock was similar to the Berbers with heavy admixture from all around, including other parts of Africa and all around the Mediterranean. So Hart isn't wrong, but he isn't completely right. The sad fact is that for much of the 19th and 20th centuries, people when making racial categories to then judge people by have usually deliberately grouped northern Africa into a different group from southern Africa and the racist stereotypes persist, even if they are completely made up and ignore actual historic patterns along with basic logic. Egypt is part of Africa, with heavy connections to and not infrequent mingling with the rest of the lands around the Mediterranean, Red Sea, Arab Sea, and even the Indian Ocean. Modern Egyptians are the mutts of mutts, so it would be absolutely no surprise if you had a whole range of skin tones for the pharaohs.