The tan wire counts as a white one. It's probably just old, and was white when it was new.
Home 120V circuit wires come as black, white, the bare copper ground wrapped in paper, and some times a red
one for applications you may not have. Such as running two circuits using one cable like in a kitchen
where different outlets are on 2 different circuits, but only one cable comes out of the panel box going behind the wall.
Call RCBS and tell them your tale of woe.
If they don't give you a new switch or thermal cut out-- they'll know what the problem is--
They'll sell you one on the cheap.