rudder refurbishing

Sand them down and paint them black or white!

what type of paint?

I have heard recommendations for "appliance paint" for refinishing rudders, available at hardware stores. I have not used it myself so caveat emptor!

i avoid painting because it will eventually become a maintenance headache, i would wet sand (200, 400, 600 grits )then polish with a disc polisher/buffer and seal with boat wax. rewaxing occasionally is a lot less work than paint maintenance and probably slicker/faster

Do you have stock plastic rudders or EPO fiberglass rudders?
The white plastic ones turn brown and a little sanding and polishing can make them look like new.
The EPO rudders have a very thin surface layer of gelcoat over the glass fabric.
When exposed to the sun for too long they can become "fuzzy".
You CANNOT simply sand these down. They just get fuzzier.
You can spray them with several thin gel coats, sanding in between coatings.
I used the one part (appliance) epoxy on my rudders several years ago and they still shine like new.
It is a very hard paint and sands well.

they are the standard plastic ones