Niobium

Niobium is a unique element, like gold or silver or titanium. It doesn't tarnish or rust, and the colored niobium isn't an enamel like the other colored wire. It's an electrically-induced anodization layer on the metal, the different colors are created by changing the thickness of the anodized layer. This means the color will never flake or come off, but it might get scratched off if you're REALLY rough on your stitch markers. You know, if you scrape them against concrete.