A slight correction... when you see the green bars, the valves are closed in the ICE which is using the energy that would normally be used to propel the car [if the valves were open] to charge the batteries. You'll notice when you let off the gas that the number of green charge bars is relative to the speed you are going due to more energy in the system to regen the battery (15-35 shows ~1-2 bars, 35-50 shows ~3-4 bars, 50+ shows ~4-5 bars).

 

The valves can also be open when you see green bars, but in that case your iFCD isn't pegged at 100mpg...