Pull the plugs out and see if the pistons are wet when the car is hot. If its cold and you pull the pistons after running for a short time fuel may make the pistons wet but if the engine is warm the fuel will evaporate fast. If any of the cyls are wet then you probably have a problem with the valve seals.
Now just to say what just happened to me, #6 cyl was wet with oil so I put valve seals in it and it started smoking a lot worse, they were cometic valve seals green viton but they did not fit tight at all when going over the valves. After replacing them the smoke was 10 times worse, and it was white, but that was with only water in the system no coolant, and for a short time with not even water in it, I drained the water out of the block and started it a few times and still smoke. Now on leakdown test I got readings of 7% when it was cold and 2% when warm.
Anyways after replacing the seals with the cometic ones all of the cyls were wet with oil. I did not buy them from cometic so they may have been knock offs but were green viton so dont know. So since all of the cyls had oil in them I put a new set of seals in them, this time felpro brown viton. They were a lot tighter fitting and you could see swelling of the viton and spring as they were installed unlike the first set I put on. After doing the seals it smoked for a little bit from the oil in the exhaust, but for the next three days it was fine.
So with no smoke for a few days I decided to do some 0-120mph runs then drove for 35 miles to a friends house. When I got to his house we went out and did some more 0-80 mph runs and it started smoking again. I drove it home and it got even worse. Checking the cyls they were all dry, so I pulled of the exhaust elbow and it was covered in oil. Moved the shaft on the turbo and there was a lot of play probably a quarter inch of side to side play. Took the turbo off and the exhaust mani was dry so I pulled out the turbo and took it apart. The bearings dug into the housing and the shaft and there were cracks in the wg flapper. The new turbo should be here today and I can get it fixed so my wife can finally drive her car. Now I just have to get a quart of oil out of the exhaust, I guess its a good thing I hollowed out the cats.
Hope that gives you some ideas. As I said enough oil burning will burn white, as will coolant, as will water, as will fuel. And on startup you can get smoke from a lot of different points. I would start by pulling the plugs and checking to see if there wet, and do a leak down test if you can get hold of a leak down tester.
