So like a poultice idea.. interesting. Sounds like good infoSome dish soaps have color dyes which is why spotting advice from manufacturers recommends "clear" dish soap. Once the surface has been thoroughly rinsed. Take some baking soda and pour over it, enough to cover 1-2" beyond edges and leave fairly thick. Add plain water to make a thick paste (that won't run). Cover with plastic and seal edges with painters tape. Leave for 48-72 hours till dry. This should remove it by wicking into powder. Works well for us!
Well it dried and appears to be nothing there. It's liquid Palmolive. That green liquid dish soap. I avoid the lemon stuff as it is harmful to granite.Ok, ok mystery spot.
Why do you say dish soap? There's lots of household cleaners that will damage granite/marble.