It's common sense, but it bears repeating around this time of year: in order to make a trade in the NFL Draft, a team must have a trade partner.
This is important to note because the majority of Colts fans seems to hope the team trades down from the 18th overall pick in the upcoming draft, and it certainly would seem to have plenty of benefit to the Colts. The question, however, is which team, if any, would want to actually trade up to the 18th pick. After all, the talent in this year's draft is deep and the talent level is pretty similar from mid-first round to later picks and into the second round. It is likely, then, that the team that would look to trade up would be in pursuit of a quarterback.
That's where the Denver Broncos could come into the picture. The Broncos pick 31st in this year's draft and they really need a quarterback. The top two at the position - Jared Goff and Carson Wentz - will go numbers one and two, meaning that the quality of talent at the position will already have taken a big hit after the first two picks. That leaves guys like Paxton Lynch and Connor Cook as potential options for some of the other teams in the first round, and if the Broncos want one of them (particularly Lynch), they may need to move up from the 31st pick to get it.
According to Walter Football (pointed out by Mile High Report), the Broncos have had discussions about trading up and are looking to do so. The only team mentioned in the article that the Broncos have talked to is the Green Bay Packers (at 27) and they reportedly want Lynch, so it sounds like both the Broncos (31st overall pick) and the Browns (32nd overall pick) could be looking to trade up.
If that really is the case, a trade with the Indianapolis Colts could make a lot of sense. Many of the teams before them almost certainly won't be taking a quarterback, as picks nine through seventeen are the Buccaneers, Giants, Bears, Saints, Dolphins, Raiders, Titans, Lions, and Falcons - in other words, unless a team takes a developmental guy to work behind a veteran (unlikely), there won't be quarterbacks going then. That would mean that, after the eighth pick in the draft (which the Browns at a pick that is a very high spot for someone like Lynch to go), it's likely that a quarterback wouldn't go until after the Colts' pick. As soon as the Colts' 18th pick takes place, however, there are a few teams that could be looking for a signal-caller. The Buffalo Bills pick 19th and the New York Jets pick 20th, and it's very possible that both teams could be targeting a quarterback.
If the Broncos really wanted to get Paxton Lynch, then, trading up with the Colts for the 18th pick would seem to be the best and safest option (though a move wouldn't come until draft night when the Broncos could ensure that Lynch was still there). The question would be whether the Broncos would want to give up what it would take in order to make such a move. According to the draft trade chart, there's no exact combination that would seem to work ideally for both teams (since compensatory picks cannot be traded this year, which limits a number of the Broncos' tradeable picks), but a deal featuring something like the Broncos' first rounder (31st overall), their second rounder (63rd overall), and then either their fifth rounder (144th overall) or a seventh rounder (235th overall) would seem to be the most fitting. That's not a cheap price for the Broncos to move up, but if they really do like Paxton Lynch enough, it might make sense to do it. For the Colts, it would seem to be a good move in order to collect more picks, something they could really use.
There's absolutely nothing definitive to this and at this point it's simply speculation, but a rumor from Walter Football suggests that the Broncos might be looking to trade up. If that is the case, a deal with the Colts for the 18th overall pick would make sense for both sides.