Heat. Chrome is not meant to deal with heat. Chrome is actually clear and the shiny part is Nickel, which takes heat just fine, melting point of roughly 2,600 degrees. While Chrome has a melting point around 500 degrees.
Polish, usually does the trick. I personally like Master Formula (have to buy on the internet or trade shows) but Mothers is pretty good too. It may get rid of the yellow/gold or may not. It all depends on if the Chrome will flake off. If it does your good. Then you just shine the Nickel up and your set.