As a casual reader of history I've always read that the people of the Maghreb were Mediterranean (i.e. essentially white). As a student I traveled to Europe and North Africa. Many North Africans I met in France looked what I, as an American, would call "black". Many looked what I would call "Arab". In Egypt I found what looked like a true melting pot. In the coastal city of Alexandria the people were fair skinned and blue and green eyes were pretty common. In Cairo the majority looked "Arab", though Cairo is truly a global city with a wide variety of colors. In the Egyptian countryside and in the south at the Valley of the Kings the people looked "black". In Cairo I spoke with a Copt, generally about politics but also Coptic culture. He mentioned that Copts call themselves "Rem en Kemi" which translates to something like "Romans in Egypt".
My takeaway from the experience is that North Africa is a patchwork. I would like to know what peoples and cultures contributed to that patchwork? Why would a Coptic Christian tell me, in Arabic, that he is a Roman?
Initially, the main groups to leave their marks would have been the Phoenicians (who famously founded the settlement of Carthage in modern day Tunisia). To the east, there were the Egyptians, and a Greek colony called Naukratis.
Later on, the Romans became the dominant power for almost 500 years, and their mark is still there nowadays. Following them were the Islamic caliphs, who conquered from Turkey to Spain, and left the mark of Islam in the region. There was also some Byzantine culture in the area before the the Muslims came through, though this is harder to see on the surface.
The next major influences in the area weren't until the European powers of Britain, France and Italy began to colonise the area, leaving amongst other things the Suez Canal.
As far as I can understand, the reason a Coptic would call himself a Roman is because the Coptic church comes from the Byzantine Empire. The Byzantines called themselves the Eastern Roman Empire initially, following Constantine's separation of the Eastern and Western Roman Empire's in the 4th Century CE. The Byzantine Empire continued to maintain a number of Roman traditions, including calling themselves Roman.
/r/arabs might also have an answer