767 here. When extending flaps the biggest effect on the amber band will be from UP to F1 when the slats extend. That takes about 5 seconds whereupon the amber band drops about 40kts. You'd be hard pressed to keep it in the amber band on purpose let alone by accident. Flap maneuver speeds are recommended anyway. Boeing also recommends you set your target speed above MinMan (amber band) but there is no prohibition on flying in the amber band either. Look what happens when you pull speedbrake.