It's perfectly natural to blow smoke when you hit high RPM's because you're pushing so much fuel. Even more so if you have an aftermarket exhaust.

Haven't you ever noticed how a cars exhaust increases just before they start speeding up. They stomp the gas, the engine goes crazy, a lot more smoke becomes visable and then the car goes faster. I now that I used to watch my buddies tail pipes when I rode bikes in a group because I could actually see the extra exhaust before I would hear their engines rev up. That way I could hit the gas not long after they did and I wouldn't fall behind.

Now if it's blue or white you should get the car checked.