Thank you very much for your questions. It looks like my thinking about the colors is a bit different. I'm at about 13.5k miles.Check me to see if my thinking is right. I have come to realize that keeping things in the blue means the engine output is sufficient to provide all power that is needed (and then some) based on the demand. Anything between the needle and top line of the blue, while the engine is running, is excess and is banked in the batteries as engine output exceeds what is being drawn to power the wheels. This may be a dirty assumption, but it's my perception after 30,000 miles.
I assume that the needle of the Power Meter is telling you, on a moment to moment basis, the total amount of power that the system is putting out. The colors referred to are just convenient portions of the meter read-out for ease of communication. At a given moment in time, and a given point on the meter dial, a given total amount of electric power is flowing. That power could all come from the battery (EV mode), all from the ICE (direct drive over 50 mph mostly) or some combination of both. Some of that power could be used to turn the wheels, some flowing back into the battery, or some combination of both. One of the screens gives you a moment by moment picture of this, and its all computer controlled.