A Wizard mentioned in Equal Rites. Properly titled "Granpone the White", Mrs. Whitlow and her staff of cleaners were having some trouble with his laundry (a stained white vest) when Ksandra arrived with Granny Weatherwax. Bleaching didn't help, and "tincture of myrryt" only turned it blue. Mrs. Whitlow had never seen anything like the stain before (although she had seen brimstone, soot, dragon blood, and demon blood stained on wizards' robes), and comments that he's "going to be Granpone the Gray soon if he doesn't take better care of his laundry..."
The annotation from a deleted article (deleted due to duplication and incorrectly spelt character name) reads:-
In the more prosaic Discworld, Grampone's progress is a mirror-inversion of Gandalf's transformation in Middle-earth. Gandalf begins as the Grey, fights a Balrog, dies, and is sent back as the far more powerful Gandalf the White, strengthened for the final confrontation with Sauron. On the other hand, Mrs Whitlow, were she to have existed on Middle-Earth, would not have let this deter her one little bit from making caustic comment on the state of his linen. Perhaps this is the reason why Gandalf wandered the Earth with no settled home: he could face down Balrogs and fight a magical duel with Saruman with few tremors, but dealing with Rivendell's housekeeper scared the good-for-the-Ents out of him.