Instead of gray, I would choose silver. I have silver racing plastic from Maier on my 400ex, and it looks great, especially if you powder coat the frame red. I upgraded to the 450R and now the 400ex is now my wife's quad.
I am making mine white when i get it. Also im getting gold wheels for it to make it look like a old 250R. I love the retro look. I am saving the fenders wheels etc. So in 15 years it will look brand new with the stock fenders.