1. Mine is like that too, but I think it also depends on how much throttle you use. When I'm cruising above FL300, with the throttles at 70% - 75%, there is a lot less black smoke mixed in with the contrails (sometimes it's almost completely white).

2. I'm having this problem in quite a few of my aircraft. It sometimes happens when taxiing too. I'm guessing it might have something to do with the terrain mesh I'm using (ORBX AU). It only started happening to me a while ago though.

Going by the Cockpit ToolTip I set my throttles at 70% and the flight is usually around Mach 0.8 - 0.82 as well. I'm not sure what the N2 readings are though. The contrail seems to have the black smoke mixed in with it, but to a much lesser degree than say when the contrail first start and the throttles are further forward for climbing.

In cruise, if I have a powerful tailwind, I pull the throttles back further and with a headwind, I push the throttles forward further, obviously and the black smoke will sometimes disappear altogether after throttling back quite a bit. I'll have to do a flight and take some screenshots to show what I mean.