My truck does this as well, only in the colder temps. From my understanding, when a diesel smoke is blueish at idle, it can be from "overfueling"(or oil). When the diesel fuel is cold, along with a cold engine Im sure that some fuel isnt buring all the way, causing the blueish visual smoke. After running for about 15 min, my truck has no smoke. Im sure the winter fuel doesnt help at all either.