I myself don't know how to do that metal color just yet. I believe a blue-tinted grey (as suggested) would work, but I've not played with it.
Re: panel lines
If they are pure black (the way I have mine), I set the entire layer to 10% on "Normal". That's 10% give or take a few % to make it lok better.
I like the way you've got it. If you want to make your panel lines darker then a few % more opacity won't hurt (I think you've got some lee-way).