Tarnish is a surface phenomenon, that is self-limiting unlike rust. Only the top few layers of the metal react, and the layer of tarnish seals and protects the underlying layers from reacting.
Tarnish actually preserves the underlying metal.
So Steve, I think this is your answer maybe.
As you wash/polish away the "tarnish" or oxidized copper(patina)
from the the case surface, that copper is gone forever
from that top layer. Over time, polishing/washing, removing
the patina or protective oxidized layer will whiten the
appearance of the rose gold because some of that copper
is gone. The Everose locks the molecules so this
can't happen, supposedly.