I don’t think it is tarnish. I have compared it with the photos I took when I first have the necklace and in the same lighting and colour temperature. It is the same shade to me.That’s an interesting point… I have not noticed as much tarnising with the Guilloche YG. So maybe it’s because the Hammered is made matte with some kind of different layer on top that makes it more prone to tarnish?
Some pieces are more matte than others. Maybe they don’t polish them as much?
The Perlée bracelets are polished.
I don’t know about others’ necklaces. It might really be tarnish for them.