The dark skinned Egyptians in Cairo are called Baladi and usually are rual Egyptians who come in from Upper Egypt. These people usually live in places like Bulaq Abu Ala. Most of the dark skinned Egyptians live in the slum areas.
In Dyanstic times the population in Luxor to Aswan was the majority of the Egyptian population. The population in Egypt going up to the late 1800's was 3 milion. Know the population has skyrocketed to 88 milion with the majority being in the Northern region. Also recent immigrants to Alexzandria and Cairo have also had their effect. Cairo has always had a predominant non-Egyptian population.