My door guards were faded almost until they were white, so i tried different ways to restore the color. So after a few tries I came upon TurtleWax Formula 2001 (super protectant with sun stop). I used for polishing all my rubber and plastic things on my car including my dash and tires. I tried it on the door guards it restored to pretty much to the original color. I waited for hours waiting to see if it would fade again like other things and it hasn't... So i suggest you use something similar to it. I haven't been in the rain yet so we will see how it comes out afterwards.
~ZumBurnouts