I´m constantly battling disc brake overheating because of a very steep down-hill on my commuting route.Bought a brand new pair of XT brakes and xt 160 rotors 2 weeks ago, they performed great up until yesterday when the rear brake started lacking power and
making an awful noise when used.The rear rotor has a sort of rainbow look to it, clearly different in color than the front one.Brake has bled just moments ago with no result.

Is this a glazed rotor?If so, can I do anything about it?Some internet articles suggested using sand paper to renew it.Any ideas?