Blue Smoke - Due to lubrication oil burning.
Reason -
Lubrication oil leakage into combustion chamber due to Head gasket broken.
In case of oil bath air cleaner, excess oil quantity in oil bath or tank.
Broken, worn piston ring.
White or Cold Smoke - There are two reason of white smoke.
Reason -
In winter season low initial temperature.
Water and coolant mixture enter into combustion chamber
Light Gray to Black Smoke
Black smoke contain unburned carbon particles (0.5 to 1 micron in diameter) and other solid products of combustion.
Reason -
Poor combustion of fuel.
Low compression pressure in cylinder due to blow by.
Operating under excessive load, i.e. injecting greater amount of fuel.
Insufficient combustion air.
Incorrect valve timing.
Smoke from car