You have two completely different scenarios. As flap extension is limited to 20000 feet, the amber band with flap represents the minimum manoeuver speed which provides 25 degrees AOB plus 15 degrees overshoot before stick shaker logic activates. As stall speed varies with flap configuration it is better to view this as 1.3 VS approximately. Above 20000 feet the band represents 1.3g before low speed buffet, ( buffet alert in FMC display ) as the stall speed is calculated using gross weight, ambient conditions and AOB. If you are flying in LNAV you have "real time bank angle protection" so the aircraft will not over-bank, ( limited 8 to 15 degrees) but if you go to HDG SEL and leave 25 degrees bank you could see the amber bank creep. The new FMCs will show you as B-buffet limited or T- Thrust limited in the CRZ page. If you are flying B-limited altitude and the ISA deviation increases, you can also see the "buffet alert" message in the FMC as you may well now be above MAX ALT for the new ambient conditions. Manoeuvring in such conditions can be tricky.