M.B.
I have the easiest solution for you! Get a Mr. Clean magic eraser. They work on everything. My sink gets yellow all the time and all it takes is a quick swipe of the eraser and it is sparkling white again.
One day I scrubbed forever with all sorts of bleach and nothing. I decided to try the eraser and it was awesome. You don't even have to scrub, just wipe!!
M.