Wouldn't it be amusing if I joked with my Asian friend about him turning Caucasian?
If I am honest with you, it sounds a bit in poor taste. Why do you want to joke with your Asian friend about turning Caucasian?
Ha.. I don't think so, I just wanted to joke about it.
You shouldn't make jokes about other people's race. This can be very offensive and make you look rude.
Relax, it's fine, I just wanted to joke about it.
It might look strange, but I am sure even if your friend is sad or mad at you, he will probably hold it in and not express it. Why would you want to jeopardize your friendship? I would probably ask how he felt about it and that it was just a joke and meant nothing else.