For all flaps-down operations (any time the flaps are not full-up) the minimum maneuver speed is the slowest speed that provides full maneuver capability, 1.3 g’s or 40° of bank (25° angle of bank and 15° overshoot) to stick shaker. The top of the amber band does not vary with g load.

Bank angle overshoot.   It's an explanation of why 40 degrees of bank is used in determination of minimum maneuvering speed; that's the slowest speed you can fly in a given configuration, constant altitude, 40 degree bank before stick shaker activation.   40 degrees is used to give a little buffer - 25 degrees is roughly a standard rate turn  (dependent on speed), and they allow for an extra 15 degree "overshoot", caused either by pilot inattention or turbulence.