If it was just dull/cloudy then I can imagine debris getting blown in that takes a while to clear via filtration, but unless you've got lots of greenish pollen (and it's usually more yellow than green) then I'm not sure where the color is coming from. I see that your waterline is blue, but is the fiberglass blue all the way down to the bottom of the pool? If so, then perhaps the green is yellow+blue (cyan, actually) so maybe the water isn't really green but is yellow which looks green against the blue pool surface. Yellow could be pollen or it could be iron, but since your pH didn't climb a lot I don't think it's metals. If you found that the color came with higher pH and went away with lower pH, then I'd suspect metals. At this point, it sounds like it might be pollen instead.