If you want to paint corner guards you should use Paintable Corner Guards.
If you paint vinyl or polycarbonate ("Lexan") corner guards their glossy finish will not allow paint to adhere to them and thus chip easily.
Paintable Corner Guards are made from a different type of plastic that provide a surface that is designed to take paint exceptionally well and avoid chipping.
Paintable Corner Guards allow you to not only exactly match your paint but also match your finish texture (e.g. Eggshell, Satin).