In military they do have to institute obedience (you can get executed on the place for disobedience) and they already has an elaborate system of costumes to wear under different conditions.
To add to these another field/office distinction would
(1) increase cognitive load,
(2) will bother those officers who work in the office since they'll be looked at as 'second-class' just from heir looks, and
(3) camo isn't unfit for the office which (as sandworm101 have noted) can suddenly turn into a battlefield if they attack the building.
Overall, one less decision to make, and that decision would only benefit those in the field. Which are, by definition, not the highest-ranking.