Early mock drafts have attempted to give the best projection at just what the Colts will indeed do with the 18th overall pick, and the majority of them seem to have the Colts addressing their offensive line. The team has a number of needs - most notably pass rush and offensive line - and those two positions have seemed to be the overwhelming consensus among the early mock drafts.
SB Nation's Adam Stites compiled a fancy chart that incorporates a number of early mock drafts (you can see the list at the bottom of this article) to see who each team is projected to take in the draft. It's a nice visual to be able to see what some of the more prominent analysts think the Colts will do with their top:
Top players mocked to the Colts:
Jack Conklin, OT, Michigan State (27.3%)
Taylor Decker, OT, Ohio State (22.7%)
Leonard Floyd, OLB, Georgia (6.8%)
Reggie Ragland, ILB, Alabama (6.8%)
Ezekiel Elliott, RB, Ohio State (6.8%)
Andrew Billings, DT, Baylor (4.5%)
A'Shawn Robinson, DT, Alabama (4.5%)
As you'll notice, the "others" category takes up 15.9% of the chart, showing that there is some degree of discrepancy and variation over who the Colts should/will take with the 18th pick. With that said, however, it seems clear that analysts think the Colts need to address their offensive line along with their defense.