generally when a diesel puffs bluish smoke on starting when cold and not starting up immediatly, it's because of poor or no preheating in the glow circuit.
check the glow heater or glow plugs and make sure they are operational. (mitsu's usually have a glow plug on each cylinder mounted near the injector)

if you have blue smoke while running (after starting) it could be a fuel problem like bad injectors or a injection pump timing issue. Also could be poor air intake like a clogged air filter.

There could be other things causing this but these are the most common.