I am saying that you have to keep the needle outside the yellow arc. That can be either without carb heat at all (on the left side) or by applying carb heat which usually puts your needle outside the yellow arc to the right side (and i say 'usually' because theoretically you could encounter situations, where applying carb heat would get your needle right into the yellow arc - it has to be quite cold then though).
If the air is really cold, there is simply no watervapour left in it that could freeze your butterfly.
Whatever is discussed here, stick to the POH (and your flight instructor).
