Blue smoke in the exhaust is almost always oil burning in combustion and white smoke (not grey, white) is normally an indicator of coolant burning off in combustion. Usually, that will smell similar to pancakes or waffles but its a toss up based on the type of coolant you use. May have a possible head gasket issue or somewhat worn rings or a valve issue (stem, seat, etc would explain the blue smoke but not the white). That is unless oil is fouling up an injector causing it to fail to close up fully, allowing fuel to dribble in. Lots of variables to investigate.
Versilon C-210-A is a clear tube that will handle the temperature and pressures of your fuel system leading up to the IP. I picked up a small spool of it a while back to see air intrusion on my trucks. Another item to note is that the most common point of air intrusion are the injector return caps. Seems people have the most issues there with intrusion, likely because of just how many joints there are in the return system.
However, I have never known air intrusion to cause smoking issues. If you get air in an injector line sufficient to effect it's behavior, it likely just wont work at all and that cylinder wont fire until the air vents out of the system. Unless of course you have air intrusion AND a bad injector where the fuel is able to just dribble into the cylinder, although that would be pretty rare.
I agree with the conclusion of air intrusion likely not being the cause. These fuel systems are designed to work with a certain amount of air in the lines. You'll pickup air and see bubbles in the line just from driving and sloshing the diesel around in the tanks. I imagine it would have to be a very serious intrusion issue to cause any ill effects once the engine was running. And yeah, for sure check the return cap. Very common point for leaking, but I don't believe they can cause air intrusion. Or I guess more specifically, if they do let any air into the line while the engine is running, it should be sent to the tank, not the IP.
I've always heard the same about blue smoke, but it's never made much sense to me. Our engines are very happy to burn and even run off of 15w-40. I would think blue smoke to be the result of any incomplete combustion regardless of reason. I'd expect over fueling or poor fuel atomization / vaporization due to improper timing, a worn injector, bad rings, blown gasket, etc; or a slight reduction in oxygen from compression leaks or a bent intake pushrod, etc, to all result in blue smoke. Of course that's assuming the cylinder in question is actually firing and the problem isn't bad enough to cause a miss or lack of total fuel vaporization. Is it just said blue smoke = burning oil because that is the most likely reason? I would love to hear your thoughts!