There are some metal jewelry that turn into green.

Copper Jewelry turns green,

Copper is a material used in jewelry because it is highly malleable and durable when mixed with other metals.

Also copper jewelry may turn your skin green because of a chemical reaction, when copper mixes with sweat At this point it can oxidize and leave green patches on your skin. The reason your skin turns green is actually a normal reaction.

Copper is a metal that’s used for a lot of  Jewelry, especially cheap ones. So, like any other copper, the metal reacts with either the product on your Body.

And that is why popular belief that cheap jewelry causes skin discoloration,

Essentially, the type of jewelry metal and it’s reaction when mixed with skin acids or body lotions generates an unsightly green hue on your skin.

Not just a Copper but Iron jewelry turns green,

When you have very low levels of iron in your body, the level of pH becomes more acidic. And The acidic environment can cause the metal content of your jewelry to react, or oxidize and cause a green discoloration on your skin.

Silver Jewelries turns green

Silver Jewelries lend themselves to the occasional green discoloration because it presence of copper. Silver is very demanding metal for making jewelry so managing there quality is important

Those are some of the metals that use for making Jewelries and turn into green after some period due to Commercial reaction.