RE: Wind indicators
I spent many years on Optimist, what a "boat"!
What you see are not wind indicators (they have a small flag on top of the mast for this use..): they help you to keep your sail correctly closed.
They have 2 "wool" stripes in each of the sail sides, two red and two green usually.. They also have a stripe on the leech for downwind side of the curse.
In windsurfing last time I've seen them was in dacron sails!! In monofilm sails I've never seen them.
I think in nowadays windsurfing they'd not be as useful as they are on boats cose a skillfull rider can "feel" the wind changes in his hands better than looking at the stripes on sail. and when wet, as you suppose, they wont work, maybe if the were made in plastic, but I'm not sure..