You have not ONE TIME discussed if Cain was cursed and marked with light/white skin (why not)? You only speak of how it can apply without specifying it. Just speak it plainly.
Both are equally possible, right?
Skin doesn't darken from the environment that quickly. People with light skin will not become black skinned people over that period of time. So that is out.
But besides that, none of this is inferred nor implied in the Bible. And it was never considered until the 1600s only when people wanted to justify enslaving black people.
So your entire conversation is not based on objectivity, but based on supporting a prejudiced mindset. It's like you're supporting a rapist argument that his victim dressed in a provocative black dresss...
It's like saying, what if the rapists were justified, because the women dressed too provocatively with a black shirt. If they dressed with a white shirt, or with a black shirt it doesn't matter. Because the fact is, the women, even if dressed provocatively should not have been raped.
But MY Point is this: The woman didn't even dress provocatively.
Your counter is "How do you know".
My response: The clothes that we've found, do not match the clothes she is accused of wearing. And you are forgetting that it doesn't matter.
Your counter is: "She could have worn a black shirt"
My response is: "no black shirts were found at the scene, and no recepits show she purchased one, and no one has ever seen her wear it."
Your response: "She could have bought one, with cash, and lost it after she wore it before the rape."
My response: "There is evidence from shirts she wore, that those shirts were the one she was raped in"
Your response: "Someone could have switched the shirts, put the forensic evidence on them".
My point is that it is as possible as any random meaningless transmutation. God could have marked cain with a unicorn on his head, or with bats attached to his ears. There is NO reason to zoom on into black skin verses ANY OTHER POSSIBILITY.
Why you spend so much time trying to explain it, where you bring in the origin of other skin colors... is because YOU are obsessed with proving to yourself that blacks were cursed. You won't let it go and you want to find a crack in reasoning that you can fit your prejudice in.
You have shown by your opinion it's not possible to you, that is correct.
You're not considering this in light of the information the other sides gives up without explanation. Such as...
Even if it stated Cain was cursed and marked with dark/black skin, this could be a description of many, many races. Because the verse says nothing of facial features. There is also the unsaid portion of this story if Adam was tanned and all of his posterity with the same facial features, then Cain's skin was darkened, long before Noah was born Cain's posterity and Seth's posterity would have mixed for a thousand plus years. By the time the flood arrived there would have been an assortment of light to dark brownish skin colours from race mixing and skin colour darkening from environment.
Point being by the time Noah came along, with everyone having the same facial features and hair type and various skin shades of brown, genealogy would have been the only way to know who was from what lineage.
Now take two thousand more years of race mixing and facial feature changes and there would be next to no way to identify who was of Cain's lineage.
And all of the above can be said in the reverse for any colour you want to start Adam with and for whatever coloured mark you want to assign Cain with.