if adam and eve were white . why are they black people?

The correct answer is that the Bible is a work of fiction and irrelevant. But if you go by the Bible, there is a real case to be made that Adam and Eve aren't the only people divinely created. When Cain kills Able in Chapter 4 of Genesis a strict reading would suggest that only 4 people exist in the entire world, Adam, Eve, Cain, and Abel. But when God exiles Cain for the crime, he is afraid that if he goes out into the world he will be killed. Well, if there are no other people, who is going to kill him? Then it says he sets out for land of Nod where he meets his wife and has children. Again, if there are no other people how the heck is there a place called Nod with people in it?

There are a couple ways to explain that, but the easiest is to say that there are other people that are created by God, but their stories are not specifically told. That is not inconsistent with the way the Bible is written, which only follows the bloodline relevant to the story from Adam to Abraham. The stories of the others children of Abraham's descendants, the the children you presume they also have, are not told because they are not essential to the plot.

So when were these other people created? Well, it could have been any time, before or after Adam. I like to think it was before because in Chapter 1 on Genesis God creates man and woman together on thr 6th day. But in Chapter 2 he creates Adam, and than Eve later. Since it never says a day passes before he takes the rib from Adam, this could just be a more specific telling of the events of the 6th day. But it is also possible that the people created on the 6th day are the people living in Nod, and possibly other places. Adam could have been created later specifically for the Garden of Eden, sort of like God's pet. Nowhere in Genesis does it specifically say Adam was the first person ever created. This could explain different races.

The problem with this is that God killed all those other people in the Flood. When he resets the world after the flood, only 8 people exist, Noah, his 3 sons, and their four wives. But it never says where the wives of his sons come from, so an easy explanation is to say they are just a very multicultural family, each with a wife of a different race.

Another explanation, and this one doesn't require you to believe any of the above, is that after the Babel incident, when God scatters everyone about the world and makes them speak different languages, he may have also changed their races. It does not specifically say that, it only says language, but it is a great way to explain why specific races are found regionally around the world.

The thing about the Bible and Genesis is that it is like the writings of Nostradamus, it is so vague that anyone who is looking for something specific can find a way to interpret it to fit what they are looking for.

The city and tower of Bable brings up 2 other great question that I like. If the explanation for everthing bad that people do is God grants free will. Why would he actively stop people from building a city and tower, and goto the drastic step of spreading them throughout the world and making them speak different languages? Sounds like he robbed them of their free will.

Second, if God knows and sees all that is and will be, didn't he know they were going to build all this? If he is going to actively stop them anyway, why not stop them before hand? But what God says when he sees them building it is "If as one people speaking the same language they have begun do this, nothing they plan to do will be impossible for them". Well shouldn't God have know already it was not only possible, but going to happen? Shouldn't he know everything they are planning to do? Why would this be a thought or concern for an all knowing God?