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. :(