Answer:
this is wrong: Black people are simply different shades of brown, which can range from pretty fairly light to dark. The "become" that way from being born to parents who have the same traits.
this is right: black people are like this because a long time ago when whites and blacks had never met blacks evolved to the hotter weather nearer the equator to block the suns uv rays and white people evolved for the cold north to protect them from the cold. If you swapped a white person and a black person in the different climates back then they would both die. The reason they don't die these days is because we have clothes to keep us warm and fresh supplies of water to keep us cool and sun protection lotion to protect us from uv rays.