My sweat cleans a tarnished penny in seconds, and the rear ramrod pipe on all my long guns is bright brass when the rest of the furniture is nicely tarnished... It also stains wood when I don't want it to. Not black, but definitely noticeable. Alcohol cleans most of it, but I'm still careful about handling when I do the final scraping and detailing on a stock.
It'll probably disappear under the brown stain, particularly since it's a dye and not a chemical stain.
-Eric