For decades, the gold and clear finishes on zinc parts ran on hexavalent chromium. It worked beautifully, and it had one small problem, which is that hexavalent chromium is genuinely nasty stuff. Erin Brockovich got a whole movie out of it. Regulators eventually noticed.
Enter trivalent chromium. Same family, much friendlier behavior. Trivalent chromate gives you the colors and the corrosion protection without the hexavalent chromium, which is why it clears the RoHS and ELV requirements that hex finishes cannot. Most new work runs trivalent now, and honestly, the finishes look every bit as good.
We run trivalent yellow, clear, and black on both lines, RoHS compliant across the board. We still run hexavalent yellow too, because some legacy prints and certain specs call for it by name, and we are not in the habit of arguing with your drawing. If your part has to be hex, we plate it hex. If RoHS applies, we steer you to trivalent and everybody sleeps fine.
The short version: the chemistry got a glow-up, the parts kept their good looks, and the planet got a small win. If you are not sure which chemistry your print actually requires, send it over. We have read enough call-outs to spot the difference, and we will tell you straight.