The reason why the tach does
The reason why the tach does not dip into the blue area on cold start while the engine is running is somewhat difficult to understand. When operating on a cold start, sitting at a red traffic light with your engine on, your battery is in fact charging, HOWEVER, the reason why the meter does not dip into the blue area is because this blue area only indicates how much energy you are regenerating through BRAKING, not by the engine. The lower the needle drops into the blue, the harder you are braking, thus the more energy you are recapturing during your braking. If your engine is running while stopped, it is in fact charging the battery. I hope this puts your curiosity to rest.