Whenits white its usually been cold, its like starting a car when its been cold.

Modern 'clean burn' engines donot exhaust white/black smoke on start ups. On the older piston engined aircraft, black smoke was emitted during start up which was a result of the excess fuel supplied while priming the engine prior to starting. Later generation pistons and jets were prone to emitting smoke till the engines picked up and ran smoothly. This also represented the residual fuel from the previous run or mere seepage after shutting down. Engines which started by firing cartridges emitted black smoke which was the gun powder residue from the starting cartridge. The B-57 was one such beautiful example. All this, however, in neither dangerous nor worth worrying about.