In his most recent mock draft, ESPN's Mel Kiper Jr. has the Indianapolis Colts taking Ohio State offensive tackle Taylor Decker in the first round with the 18th overall pick.
It's hard for me to see a situation in which one of the top three offensive tackles is still available here, but Decker is a solid value at this slot and I don't think the Colts can go wrong with a "best offensive lineman available" strategy, potentially more than once.
I'll say this for Kiper: his reasoning is the most straightforward and honest explanation that we've seen from a mock draft that has the Colts taking a tackle in the first round. Most analysts simply say that the Colts desperately need help at right tackle (or something like that), but Kiper simply says Decker is the best offensive lineman available in his mock draft, so he has the Colts taking him. It doesn't mean that it's the best pick possible for the Colts at number 18 overall, but it does at least give the honest reasoning for people mocking a right tackle to the Colts: analysts look at the Colts' need along the offensive line, look at their draft board, and assign the best remaining lineman to the Colts. That's what other analysts are doing, but at least Mel Kiper Jr. is honest enough to admit it.
Decker is a good lineman who was a three-year starter for Ohio State, playing in 54 games and starting 42 of them. He was an All-American in 2015 and helped Ohio State win a National Championship in 2014. He spent most of the time at left tackle, but he could move to the right side of the line in the NFL if a team were to want him to (and if the Colts were to draft him, it would certainly be as a right tackle).
Ultimately, the Colts' biggest need is at pass rush, but offensive line is certainly a need as well. Along the offensive line, though, the interior is the biggest need - such as the center position - and while the right tackle spot could stand to be upgraded, it's not nearly as big of a need as some of the others.