Hello!!
The paint pigment might be chromium oxide green, which is the color by nature and is very stable. It would explain the good colour on the relic.
For the chrome green pigment colour see for example:
https://en.wikipedia.org/wiki/Chromium(III)_oxide
Or do Google image search with the chrome oxide green.
BTW (Zinc) chromate green is completely different colour and pigment (mix).
Cheers,
Kari