Some Tetrarchs (possibly all, though it's impossible to be certain) were camouflaged in a banded olive drab & black scheme. Some might well have been plain olive drab, but there is a photo of a camouflaged Tetrarch wreck in Normandy, so at least one of them was camouflaged and it therefore seems very likely that the whole squadron was similarly camouflaged.
As Emilio says, Vallejo's 'Russian Uniform' is a pretty good match, but I would use it as the final 'highlight' coat – don't make it any lighter. I use Humbrol 159, which is a touch darker than Vallejo's 'Russian Uniform,, but is still a bit too light.
The dark earth & black camouflage scheme often seen was the obsolete mid-war scheme and had almost certainly been painted out by D-Day. The brown & green scheme is simply wrong, but it's on the Tetrarch at Bovington (the restorers for some reason mistook the dark earth & black scheme seen in black & white photos for green & brown), which explains its undying popularity among wargamers.
Markings:
Formation sign was the Airborne Forces' Pegasus & Bellerophon sign in sky-blue on a maroon square.
Arm-of-Service sign was changed before D-Day to the standard Infantry Division Recce Regiment sign of '41' on a green-over-cobalt blue square.
6th AARR did not use the usual geometric squadron signs in Normandy, but instead painted the troop designation (HQ, 1, 2, 3, 4 or 5) in quite large figures on the turret rear 'quarters'. These were either painted in white or sky-blue – the jury's out on that one, but Airborne units frequently vehicle registrations and other 'white' markings such as AoS numbers in sky-blue.
paints 
