The first assumption is that Adam was only one of the races that we see today. That may not be correct. Think perhaps...Oriental eyes, brown/black skin and red hair...Eve? reddish complexion with blonde hair. when they had offspring? The offspring were ruddy with black hair (recessive genes bloomed) and blue oriental eyes, etc. True, God said 'after their kind' but we really don't know what that looked like, do we?