As it pertains to career mode, the green flare shot at your airfield from the vehicle signifies you're clear to takeoff, and then the white flare means you're clear to land.
Thank you gents! When flying in career mode; and you are not the flight lead, the AI flight lead will always give go-ahead with the green flare? I've noticed sometimes he does and other times he does not. I usually just take-off and they then do the same. Perhaps I should just wait for the signal then.
In multiplayer; are there standard meanings for the different colors? I thought I read somewhere once that red meant attack.