The responses you received mostly apply to gasoline engines. The theory of a diesel engine and many of it's traits are totally dissimilar to their gasoline cousins.

Black smoke means that there is unburned fuel. The most common cause is dirty injectors, which have a spray pattern that is not uniform, causing incomplete combustion.

A tired engine, with blowby or worn guides allows oil in the combustion chamber. This will be burned as fuel to a certain point, when the engine really starts pumping oil the injectors get really crudded up causing this problem.

The second most common cause is, in the case of a turbo an incorrect ALDA adjustment or a problem with that system.

The third is a problem with the injection pump.

Blue smoke is of course an indication of so much oil in the combustion chamber that it cannot be burned and comes out the exhaust. This is more prominent in a gasoline engine because oil will be more easily combusted in a diesel engine rather than make it out the tailpipe.

From your description, it sounds like dirty injectors are the culprit, but you won't know until you start eliminating things. The first step is typically injector cleaner. I ran some through my daughters car after the engine overhaul. It's not perfect now, but it helped alot. The engine was sucking so much oil before the overhaul that the injectors were a real mess. Maybe I'll break down and replace them.

Have a great day,