Now that the days are getting longer and I can do critical service work without a flashlight in 9 degree weather, I can see a brown ring on my brake rotor. The caliper failed on this side.
I dont think my failed brake caliper siezed on the rotor and I dont think my brakes were stuck in a locked braking position and the brakes were not literally smoking.
I think the brake piston got stuck in the retracted postion and ceased to function and provide braking pressure.

Nevertheless my Rotor has a brown ring on it. Should this be indicative of a failed rotor and thermal discoloration? Or is the brown ring a sign of some less severe condition. I always though thermal discoloration of overheated high carbon steel was Blue and not brown...

Brown discoloration on Brake Disk Rotor 83 240D