lemon-yellow stain on granite (Colonial Cream)
We have a granite countertop (Colonial Cream, reportedly a very porous granite, but well sealed). We have kept a large soap dish on it, with a white towel between the dish and the countertop, for a couple of years. The dish was moved for cleaning the countertop, every couple of months or so.
Nothing happened until recently, when a bright, irregular lemon-yellow stain appeared under it.
Now I know that stain removal starts with identifying the source of the stain. In this case we don't have a clue. The towel was dry but could possibly have become wet in the past from water spilled nearby. The color is nothing like the reddish-yellow color of iron. The area is still waterproof (unsealed areas turn brown upon becoming wet; this area doesn't).
I have tried #40 hydrogen peroxide with ammonia (Windex) and also bleach (separately!). Perhaps there is no reason they should work if the area repels water, but anyway they didn't work.
Any suggestions appreciated.