You might try one of the commerecial teak cleaner/brightener kits such as the one from StarBrite - available at West Marine and other retailers (no affiliation with the maker). It has an acidic cleaner which might cut out the rest of the stains and the restorer/brightener will help with the color. If you are still not happy with the end result once it has dried it may be time to break out the sander.
