Rob,
You can leave those light guards off as well if you are doing a military version as well,
MLB63,
The "grey" bumper is most probaly metal alot have the paint missing or never been painted and the metal dulls very quickly.
As for colour many ex-forces ones get a re-paint by their new owners so no hard and fast colours paint job might not be a pristine re-spray unless they blast it back to bare metal even then there will still be bashed bodywork. the interior seats will be pvc covered so either matt black or possiably a satin black however
some may have had racing seats fitted if used for off road racing, the tarps will almost be khaki colour
most are this it's just the dirt and weathering that makes them look O/D.
If you want to do something
a bit different try a google search for ifor williams
they do a range of metal hardtops for rovers and scratching one shouldnt be too hard,
BTW I've seen some army Rover (0-shortbase fitted with rollcages and recaro sports seats and a load of lucas spot/foglamps these were used by unit/corps rally teams
Off topic but worst job I had to do on a landrover was scrape red-lead paint off the rear compartment of an FFR (fitted for radio) with a butter knife

they had to have this done every few months to inspect the metal underneth as the batteries had a habbit of leaking acid
there were a few of us doing it that day at the school of Mech transport we couldn't go on Easter leave until it was done

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