Hi,
Average completion defines the completion of your game without quitting or disconnecting(opponent or by yourself).
Green signal defines, 80-100% Completion.
Now if you are yellow, want get back to green, I would say from my experience, play blitz (53 games to be precise) without getting disconnected either by you or your opponent back to back. Blitz was they way I got back from yellow to green. Don't know about no of games in strokes to get back to green signal.
I guess green, yellow or orange won't impact the difficulty of your game, but it will impact getting a game to play with. Most of the people prefer, green signal to play with, yellow a little less, n orange a lot less.
Thanks