It is normal. The Full Gauge refers to all power available (Electric + ICE). The Blue window means the maximum power you can obtain in EV mode. If you accelerate hard, the power will need to come from the ICE. That´s why you will see the gauge coming blue, while inside the window, and turning into white when ICE turns on (and probably the battery icon will start recharging). If you floor the pedal, it comes amber (yellow) telling you that the car will be using both engines (ICE + electric).