Black smoke can also be from bad nozzles which aren't spraying (atomizing) the fuel enough, so all the fuel doesn't get burned. If the engine smokes a lot of black smoke at start up after an overnight sitting, then the injectors are probably "leaking down", i.e., leaking raw fuel into the cylinder(s) during the hours of shut down. Usually white smoke indicates water vapor in the exhaust (Poss. head gasket leak or cracked head). Joe brings up a good point, though. If the smoke is just a short time event, you are probably OK. And, finally, bad fuel can cause a lot of smoke. The next time you get fuel, try a different station or brand of fuel.
Paul 1987 300 SDL; 2000 ML; '69 MGB; '68 VW Fastback