Evolution is taking care of that. You're just trying to rush it a bit too quickly. I am imagining in about 400 years, everyone will look the same: a bit of asian looks, a bit of caucasian looks, a bit of negroid looks, a bit of hispanic looks (whatever that would be). Everyone's skin will be a bit darker than the lightest skin tone today. Everyone will have smoother features and fewer jutting jaws and peaked noses.