Definitely removed the colored chromate finish on the latch. Not surprising, the chromate finishes do a good job enhancing corrosion resistance but they are pretty delicate chemically. And yes, extremely thin ... in fact not even really a coating, but an alteration of the surface of the zinc plating.
As of yet .... I don't have a plan
Since it appears the base zinc plate is good, and the phosphate in other places .... might just buff it up some and oil it down. Anything else would probably require taking it apart, and I'm not sure I'd be able to get it back together in a way that looked original.
I could try dipping it in gold chromate solution and see it it takes on the zinc plated parts. It shouldn't have any effect on the phospated parts I don't think.