Preferred color pkgs should be erased last

Preferred color pkgs should be erased last
- On install we need to queue preferred colored pkgs before others
  to account for the way colored files get laid on disk. On erase,
  we need to revert this for the same reason. Most of the time
  dependencies take care of this, but the queue placement matters in
  cases such as RhBug:680261 where the order is not dependency-driven.