reporting back:
i've tried all except the paint and copper plating.
rust changed the color pretty good, tho it's not really the color i wanted. copper burnish worked too, and it made my scrap shine with a tint of copper red. but i think the greatest success is in tempering, or "blueing". the steel turned into shades of bright purple-ish red just before turning blue.
i shall have some pictures up eventurally, right now i couldn't get my camera to capture the shininess of it... =