Transparent,clear - most likely what I see described as sunblock/skin oils in other posts. Only visible when I can see light reflecting off it. When I skim the bugs etc off the surface it shows up on the netting as a brownish scum as it piles up on itself. The water return nozzle points right to the middle of the pool so there are a couple of still areas on the surface that allow it to sit unmolested.

Now that the pool chemistry seems to be in a regular routine for me (thanks to your site) this is really the only issue besides a tiny hole I found today in the liner. I can continue to swipe away the scum at cleanings but was looking for alternatives...