While there are biological reasons that may explain why people living in the North of Europe lighter skin than those living in the Equator, those reasons aren't important enough in their own to make the existance of "Black" colonies in the north impossible (even in primitive times).
The Americas have both very hot regions and very cold regions (like Alaska or Tierra del Fuego) and in all cases the colour of the peoples was more or less the same (as far as I know).
The Americas were probably colonised somewhere between 50000 BC and 9000 BC. Yet the diverse climates and the diverse amount of light the different regions recieved wasn't an obstacle that humans couldn't overcome. ALL regions were colonised why the descendants of the same people, without experiencing a significant change in the colour of the skin. In fact, the Spanish were surprised not to find blacks in the West Indies. Ant the Fuegians weren't precisesly blonde.
Maybe this would have changed eventually. According to the Spanish "Cronistas", some Indians were darker than others. But, as the populations moved, there wasn't enough time for a group`to adjust its skin colour to a certain area. Humans move and progress waaaay faster than the rythm of evolution.
All this is to say that there's no biological reason why Blacks couldn't have established colonies in the North. There are a combination of historical and enviromental reasons that explain why that didn't happened IOTL. The biological factor wouldn't be enough to counter the "forces of history", if those had pushed history in a different direction.
If, for example, Africans had better crops, and had domesticated earlier; if Africans or Melanesians had disovered the Americas prior to the Europeans; or if a plague reduces the white population in far greater numbers than the black one, we might see Blacks "colonizing" the North and the far south. The fact that they'll recieve less light wouldn't have stopped them at all. Eventually, in tens of thousands of years, their skin might get lighter. But only in the very long run, and if these people don't move South, and no Southerners move North.