Mark, I've used the POR-15 'Metal-mask' paint on my rear and many front-end components. It's a metallic paint, brighter than 'cast-iron' paint. More of a silver color, but with no gloss. It looks good on items like tie-rod ends, but I would not use it on a gas tank....it'll look like its painted. I should have pics on file. e-mail me if you'd like pics.
If I were doing a gas tank, I think I would use a metal-prep to etch the surface, then give it a light coat of matte clear. But I'm not there yet....