The saints can win if they stay mostly in the air. The Colts are a small fast front line that has been succesful stopping the run. But their weakness is the passing game.
And if the Saints don't blitz, Manning loves to play against the blitz. He will do a no huddle quite a bit. The Saints have to be sure not to get caught with 12 men on field.
If they can do this I see a 35-21 win for Saints
If not I see a 35 or better for colts and Saints 21