I did not say all, or all cases. I said the extreme dark Horners have a higher chance of recent Nilotic ancestry than light skin Horners having recent Eurasian.
Doubtful, I would say. You see people on both extremes in the same family. I know of two full-blood sisters myself where one is "lightskin" and the other is damn near coal black. In my own family my paternal grandmother is very light-skinned whereas my paternal grandfather was very dark and yet I know for a fact there is zero genetic difference between the two. Same goes for my parents who are on opposite ends as well. It's normal variation among Horners usually.