Light corrosion of stainless steel or “tea staining” is a brown surface discoloration which does not affect the material structurally, but is unsightly.
All metals are prone to tarnishing due to oxidation. Chrome is a very high-shine metal, so any smudges, grime or rust are visible. However genuine chrome plating is also quite tough so it can be cleaned to ensure that it maintains its mirror-like finish. Chrome must NOT be polished - it must be cleaned - once scratched, you live with it or re-chrome it.