Over-rich mixtures burn black.
A motor with bad valve guides and/or rings gives off blue.
White is indicative of water. Could need a new headgasket, but white steam at startup is water condensation in the exhaust pipes.
Assuming that you are using antifreeze in the radiator (and not straight water), the glycol in it has a distinctive sweet smell after it passes out through the exhaust pipe (same smell as when an engine overheats and "spews" coolant).