RAF Mustang III's (P51B/C) had the same interior colours as the USAAF aircraft. The entire cockpit was finished in Interior Green, with the seat either in Medium Green or Olive Drab. The instrument coaming/shroud was dark green. later Olive Drab.
The wheel wells were clear laquered bare aluminium, with the exception of the outer face of the main spar, forming the rear 'wall' of the wheel bays (not the gear-leg well), which was yellow zinc chromate. The clear laquer was also applied to the inner faces of the wheel well and gear leg doors.
However, if the aircraft had passed through a M.U., or a (U.S) B.A.D., it is possible, though not definite, that the wheel wells may have received a coat of green zinc chromate. As with most aircraft types, there were variations, but the above is as near 'standard' as it is possible to ascertain.
This information has been confirmed to me by a former RAF pilot who flew Mustang III's, IV's and IVa's (P51K) during WW2.