Black finish?

Hi, What is the black finish that is showing up on white gold rings?
It is often on pave sections where the white gold area is shiney
black. It appears to be electoplated on. I have plated gun metal
black on yelow gold rings to get the same look, but it doesn’t work
as well on white gold. I would never plate it in an area that would
take so much abraision like the rings I am seeing advertised. What
is it, pray tell. Mark