A rich-running engine (too much fuel) can cause black smoke. You may also experience rough running, stalling, and poor fuel economy. Black smoke can also be a result of soot accumulation on the tail pipe—possible causes include a leaking fuel injector or fuel pressure regulator.
Excess oil in the combustion chamber—generally caused by worn rings or valve guides—can cause blue smoke. Over time, the spark plugs can develop deposits due to excess oil consumption, resulting in a rough running engine.
Gray smoke may be noted on hard acceleration when excess carbon deposits burn in the combustion chamber. It's normal for carbon deposits to build up in the combustion chamber when the engine is not pushed very hard. Then, when the engine is pushed hard, the excess deposits will burn off and cause the gray smoke.
Thick white smoke
White smoke may be produced when there is coolant or water in the combustion chamber; this is usually caused by a blown head gasket or cracked cylinder head. The coolant smoke will have a sweet smell and dissipate fairly quickly. This is generally accompanied by engine overheating and rough running.
Thin white smoke
While the muffler and tail pipe warm up to proper operating temperature, condensation in the exhaust system will cause thin, white smoke. You may also notice condensation dripping from the drain hole in the muffler. This is normal and the smoke will dissipate very quickly.
There are two lesser known causes for thin white smoke. One would be a severely leaking fuel injector (raw gasoline may be seen dripping from the tail pipe) and the engine will generally run rough. The other would be a transmission vacuum modulator leaking transmission fluid into the intake manifold. Transmission fluid will not have the sweet smell of coolant and dissipate more slowly. You may that notice the transmission is not shifting properly.