This is on my list of things to do for my new pool but it hasn't bubbled to the top yet (the list seems to grow instead of shrink) so I haven't actually researched the paint part. My guess is that about any water-based outdoor paint would be fine so long as it was put on thick enough to completely block the UV. I'd be wary of using oil-based paint on plastic. Plus it tends to mildew worse here in the hot, humid south