Sorry for bumping an old thread but I've noticed this with my shadowline trim as well. I'm not sure where it's from... recently had the car in for service and they ran it through their carwash so maybe there.
On sunny days it creates a sort of oily-multicolored water drop effect and it's really weird feeling. It's not smooth at all, it's like the opposite, kind of like when you eat spinach - that feeling on your teeth. I'm not sure if it's something that's on the trim itself or if something has eaten away at the coating of the trim, here's some pics. I tried some regular soap and water with a microfiber cloth but it didn't really help it.
I'm not sure how long it's been like this, but I only noticed it in direct sunlight. Even in direct sunlight, I have to stand at a certain angle to see it, so if it's not sunny you probably won't notice it.
Any ideas?