Adam and Eve carried all the genetic diversity in their genomes that all the people, (races) of the world came from them. Since dark colours (eyes, hair, etc) are dominant, that likely means the first people were dark, or darker! The lighter genes were carried recessively, and were expressed after the flood, when the sons of Noah and their children spread out into the world.
Since those recessive genes became the main ones in northern Europe, Caucasian became the main race. Likely the need for more Vitamin D in northern climes selected for lighter skinned people to survive. It may be that in places like Africa, where the sun was hot, darker skin served as a protection, selecting the darkest skin people for survival. Hence, black was expressed every generation, like black hair among Asians. (This is NOT macro-evolution, but micro-evolution - change within species, not from one species to another!)
I can't fathom how anyone could imagine that Adam and Eve were Caucasian. They carried ALL the races in their genes. That was handed down to their children and then their children, until the bottleneck after the flood, when only the genes Noah, his wife, sons and their wives carried were left to hand down their genes.
For more info:
https://carm.org/where-did-different-races-come