Prop may not have been torqued properly to begin with, or often, things just need to be re-torqued after a bit of use. You're supposed to re-torque wheel lugs and such after a few miles, though few do!
Color difference may just be that more light comes through the engine tank, changing its appearance. When my ETEC was delivered, they had used the XD100 from one of the 2 gallons I ordered, so I was sure that was what was in the engine.I seem to recall that the oil in the engine tank appeared a bit different, but can't say for sure. I wish I had my boat handy so I could take a look, but not until next week.