The 3 backs all compliment each other well and fit into nice roles within the team:
Gray - general/starting back, get off to a good start on first down etc.
Blount - pounder, can close games out in the 4th or punch it in from a yard out/convert 3rd/4th & short.
Vereen - change of pace & pass catcher.
So I'd start Gray and use Blount & Vereen in a rotation, this is a game where running 40 or so times is going to be the way to go.
The Packers are 30th in the league against the run giving up 136.7 yards a game @ 4.5 per carry. Compare that to the Colts who are 17th in the league giving up 109.9 yards a game @ the same 4.5 a carry - and that includes the beat down New England gave them. A gameplan of running all over the Packers helps in 2 areas, it keeps Rodgers off the field and it goes directly up against the Packers biggest weakness.