If he is out for the season, this is a big loss. Colon was probably the best run blocker on the offensive line, and I think last year was easily his best year.
I'd expect that Essex and Scott will probably compete for the starting RT position. Not encouraging. I think Foster plays guard because his feet aren't quick enough for OT.
Aside from Willie Anderson, there are some other veteran options out there. Flozell Adams was released by the Cowboys. Not sure if he is going to retire, but perhaps the Steelers can get one more season out of him. Mike Gandy is a FA, but he ended last season due to a sports hernia. If healthy, he would seem to fit the mold of serviceable veteran. Ephraim Salaam is also out there.
Finally, just to tweak JOM, it looks like Levi Jones is a FA, if he hasn't retired. Of course, this might not work because it would prevent the resigning of Joey Porter on the Steelers reunion tour.