Element different colour after boil

The magnesium oxide is the electrical insulation which is inside of the metal tube of the element. None of it is exposed on the surface. If you have a plated element, then it likely has a copper layer plated under the outer layer (which could be nickel.) If you removed the nickel, then the pink may be the copper layer. If you paid for stainless, you got cheated. I'd contact Amazon for a refund.

There's also the possibility that the acetic acid (vinegar) dissolved some of the copper from the chiller, which redeposited on the surface of the element, making it look pink. Not sure if that reaction is favorable for the half cell potentials of the metals involved.

Brew on