Trust the green one, it is updated via scanning for network availability.
As far as I understand it, the grey graph is based on whether or not you are connected and may include all available adapters. Sometimes if I am downloading something heavy on another pc in my home network, my grey network icon shows the circle (trying to connect); but the green one shows a good connection is AVAILABLE for me to use. It's just that my other PC (connected via LAN) is smoking all my bandwidth and confuses the grey icon; but the available wireless signal (green) is still strong.
hope this makes sense.