According to jeweler Robindira Unsworth, vermeil tarnishes. However, she says that the tarnish is natural, and that "it adds character to the item" and "makes it as individual as you are."
About.com defines vermeil as a base of sterling silver with a coating of gold that is at least 10 karats and at least 2.5 microns thick. The gold coating eventually wears off, which exposes the silver underneath; the silver tarnishes as it is exposed. The coating wears off quickly on rings that are worn every day, but necklaces and earrings hold onto the gold for a longer amount of time. Protecting the vermeil's gold coating helps to protect it from tarnishing. For this reason, jewelry designer Katrina LaPenne recommends not exposing vermeil to rough surfaces or water. Unsworth notes that chlorine permanently damages or discolors vermeil, and chemical jewelry cleaners may strip the gold off of the vermeil.