I am smiling Sue but I think you are over complicating it.
To me I believe it makes sense all people were of middle eastern colour with one language up to Babel. When God spread the people(s) across the world, having mixed there language, he again did so male and female. He could have changed their colour etc at that time, or they could have been spread east, north, south and west as he wished, then subject to temperature and time in the sun they gradually changed colour. Nothing is impossible for God as we know.
But looking from Babel we are talking 1000's of years, people didn't travel like we do today, hence the change on colour and complexion.
This comment worries me sister... Now Where the black race came from is confusing to me. Supposedly a result of a curse from God? due to sinning of some sort by someone?
I think it is dangerous to say they could be black due to sinning of some sort, what about yellow and other colours. We are all God's children but not all children of God.
I feel it is more likely, though we don't know, that those in the sun longest, south Africa etc, changed colour due to the heat and sun, they will have married people of their own colour and over time built up a resistance to the sun as a result.
Travel only increased over time, then due to industrial revolution people headed towards cities, boats took some people from country to another country but it was limited and more likely in the last few hundred years. It was then that mixed cultures started, but many still kept to themselves, birds of a feather flocking together.
But, then came the aeroplane, from the 1960's travel has increased incredibly, and year on year from then on. This meant people can go anywhere they can afford, to live or to work, mixed cultures grew and relationships (not always marriage) meant children were of mixed colours, mixed faith, etc.
No matter what happens in the world, no matter how mixed up it gets (has got/will get) I love the statement...
We are all God's children, but not all children of God.
Bless you