Rust-Oleum does make a plastic paint, and it works great.
I never used it for a pool skimmer, but I used it for a barbie jeep. We had one of those power wheels Barbie jeeps - all pink and white. The kids out grew it but it still worked great. I took it all apart, and repainted it. Black trim, brown "leather" interior, and a camo exterior and then gave it to my nephew. That paint held up to 4 years of outdoor use before he got to old for it and they gave it away. As far as I know, it's still out there somewhere driving around.
As far as making the plastic white again, go on you tube and look up "restoring old plastic electronics" there is a whole community out there that restores old computers and video games, including bringing back the yellowed cases. there are a variety of methods that can be used.
-dave