We have to realize that Adam was so much more intelligent than we are. We are even told that we don't use much of our brain power. Imagine a human who could use all of his brain power. It was certainly no problem for Adam to name and remember animals on one day. We can't say for sure, but I suspect Adam had a middle-brown skin colour.
All humans have the same skin colour.
We have a pigment called melanin. In The Answers , it is explained that from two people having the right mix of dominant and recessive genes for the amount of melanin, all shades of colour in humans could arise. Thus, if Adam and Eve were both a middle-brown colour, all shades from black through to white could be accounted for in their children and future generations. For the same reason, Adam and Eve probably had brown eyes and dark hair. Therefore, if Adam, being the federal head of the human race, disobeyed, all of his descendants would have to suffer the consequences.