For those of you who had this option dealer installed (without a choice)...

I'm noticing the fuel door is getting kind of grey/olive colored - I'm thinking the wax I'm using is doing this. It used to be a nice match for the silver paint, now it sticks out like a sore thumb. It needs to be cleaned properly, but I have a couple of questions I'm hoping you can help me answer.

- what kind of metal "alloy" is this made of? (am thinking it's not straight aluminum, as aluminum doesn't usually tarnish this way)
- it is clear coated? (though I would guess not because of the apparent color change)
- what have you used to clean it? Results?
- what would you NOT use to clean it?

Thanks in advance for the help!