The best trade back for the Cards is not with the Colts but with the Seahawks.
Geno's contract doesn't take them out of QB at all. It's really a 1 year deal. If they like one of the QBs they have to get above the Colts. If they don't take QB this year odds are they don't get near top 5 again.
And the Seahawks have a tonne of draft capital.
Round 1, Pick 5
Round 1, Pick 20
Round 2, Pick 37
Round 2, Pick 52
Round 3, Pick 83
Round 4, Pick 123
Round 5, Pick 153
Round 5, Pick 156
Round 6, Pick 198
I don't think the Colts take Will Anderson. The risk is that the Colts trade back with someone else that wants Anderson like the Falcons.
But trading back to 5 is the best mix of additional picks and a shot at Anderson.