In gold-fill there’s a thin layer of gold laminated over brass. As far as I know of you overheat gold-fill the brass seeps through the thin layer of gold and turns the metal pink. I don’t think there is anyway to remove the pink once gold-fill has been overheated, but I could be wrong?
If you want to try hydrogen peroxide and pickle to remove the pink, Bill Seely from Reactive Metals wrote a thorough explanation of how to mix it in this thread from 2012. I’ve never heard of a vinegar and hydrogen peroxide mixture, but I’ve used this hydrogen peroxide & pickle mixture many times. It works well to remove the pink from brass.
Maybe someone else has other suggestions.
Best of luck!!
Jeff