Blue is oil, white is coolant. Neither sounds good. Head gasket possible. Remote possibility of turbo seals, but that's usually blue smoke only. Oil pressure fluctation isn't good either, sign of a failing oil pump or possible bearing problems. Worst case scenario, you could be looking at engine replacement / overhaul.
Some older light duty automatics had a tendency to suck trans fluid through the modulator if so equipped, this would cause similar smoking to what you are experiencing. Not sure if your trans has one or not, as diesels do not generate vacuum for a typical vacuum modulator, but another possibility. It wouldn't have anything to do with oil pressure fluctuation though. Gauge is is a possible bad sending unit or wiring problem, but I doubt it, not that common.
Injector failures have been known to cause white smoke, but not blue that I'm aware. Might try some fuel additive to see if it helps?
"Cheese Wagon" <firstname.lastname@example.org>
Former owner - 1989 Ford B700 64-pass Blue Bird (Rest In Peace, Cheese Wagon)