UPDATE: People in the comments seem to think I'm advocating for trading back. I'm not necessarily. I'm just shooting down the argument that if we did, we could land a pair of 2nd round picks.
Recently, I've seen a number of comments suggesting that the Colts should trade back in the Draft in the hopes of getting "a couple of second round picks." This is absolutely impossible unless we package another pick or another player. To see why, consult the trade chart, available here.
The Colts' first rounder is worth 740 points, which means to pull this trade off we'd need to find a combination of 2nd round picks worth roughly that much. However, we can't just target any two picks. We can only attempt to trade for an existing pair of 2nd round picks. That leaves us only with Cincinnati's pair (37, 53) and Miami (42, 54).
Let's start by considering the better pair: Cincinnati's 37 and 53. From the value chart, those picks are worth 530 points and 370 points, respectively. The total is thus 900 points, a full 160 points more than what our first round pick is worth. We'd have to package our 3rd round pick (worth 160) to swing that trade. We couldn't package our 4th because it's only worth 58 points. Even in conjunction with our 6th it's too little. The result is that instead of 1, 3, 4, and 6, we're left with 2, 2, 4, and 6. We'd be moving back 12 spots with our top pick to jump forward 33 spots with our second overall pick. The problem is that we'd be moving back in the hopes that someone we really want would be available much later in the draft. If there isn't anyone worth taking at 24, it may be worth it, but there's no way to tell whether someone else we really want would fall to us at 86. But, if we instead compare this to a trade for a 2nd and 3rd (discussed below) all we're really getting by giving up our existing 3rd is the chance to move up from 86th to something like 71st; we'd be giving up our 3rd round pick to move up in that round by less than 20 spots.
What about Miami's pair? Miami picks 42nd and 54th, worth 480 points and 360 points, respectively. The total now is thus 840, still 100 points more than what our first rounder is worth. To pull this trade off we'd need to package our 4th, 6th, and something else because that still leaves us about 25 points short. Grigs might be able to swing that, but I'm not sure we'd want to be left with only 3 picks in the draft--2, 2, and 3.
All this said, if we trade away our first round pick, I'd much rather it be for, say, the top 2 (33), 4 (97), and 5 (129) or for something like the 7th pick in the 2nd (39) and 3rd (71) (both worth 745).