Nah, the dude above is right, white smoke is water/coolant. Black smoke is fuel... look at a modded skyline when they are fanging it. Between gear changes they will have a good puff of black smoke, this fact is eccentuated by the fact that many have atmospheric(spelling) BOVs that trick the engine into thinking there is more air in the engine than there is, thus causing it to burn a rich mixture.

well it could be the turbo seals about to let go too, but i agree with you windex that white smoke is water/coolant.
i always thought rich mixture was brownish though?