I liked this kid and saw him as a mid to late 2nd rounder who does well in zone (better than man). Unfortunately, he tore his ACL at Senior Bowl practice.
One thing that has always bothered me is that the Steelers seldom take chances with talented kids who are injured or perhaps had some behavioral issues (e.g. Burfect). Once in a while you will get a gem with a 6th or 7th (Beachum) but far more often you get a David Paulson. Rookies do not play for us much anyway, so why not use a 6th or 7th on Colvin, let him rehab in Pittsburgh while attending practices and meetings, and then see what he can give us in 2015. If he comes back at 100% (which happens more and more because they are getting so good at rehabbing these injuries), it is like getting an extra second round pick.
It seems like a low risk/high reward scenario but we seldom do it.