Here's one very good source I put credence in:
Luftwaffe Interior Colors
by Doug Nelson
PART 1-- COCKPITS
Reichsluftministrium regulations state that prior to November 1941, cockpits/crew areas were to be RLM Green-Gray 02, with the exception of instrument panels which were Gray with black instrument faces.
After November 1941, all cockpit/crew areas visible through the glazing (windows) were to be RLM Black-Gray 66. Instrument panels remained as previously stated. Fuel lines were yellow, oil lines were brown, coolant lines were green, oxygen lines were blue and fire extinguisher lines were red. However, as with any military regulation, variations of implementation and interpretation were often seen. The following is a general guide of specific aircraft by type.
PART 2 -- WHEEL WELLS, ENGINE COMPARTMENTS, ETC...
Regulations for these interior areas were standardized, and not a lot of variation existed, except for late war fighter aircraft. This variance in the latter stage of the war was caused by a number of factors. One was due to the allied strategic bombing campaign, which caused production of aircraft to be decentralized, leading to differences depending on the subcontractor of the specific components. Another was the urgent need for fighters, and the haste with which they were produced, which caused some relaxation of compliance with official regulations in order to speed up
production. Another consideration was the remanufacturing of aircraft, in which case whole assemblies were repainted at the same time. Where variations are documented, they will appear listing the type of aircraft they were seen on. As always, this is a general guide, and your best verification will be your own reference material.
Fuselage
Prior to fall 1942, aircraft fuselage areas (with the exception of the cockpit) were finished in RLM 02. After fall 1942, they were left unpainted. The Alcad used for aircraft skinning material had electroplated finish to prevent corrosion, which gave it a golden sheen, similar to that on the interior of soup cans. Aluminum and other alloy areas were still given a coat of RLM 02 to prevent corrosion. However, galvanized steel was left unpainted. Equipment such as radios, fuel tanks, oxygen bottles, etc. were in the color applied by the manufacturer. Radios were usually black or gray. Fuel tanks were usually black or gray. Oxygen bottles were usually overall blue, or painted with blue stripping.
Wing
As with the fuselage, prior to fall 1942, wing areas were finished in RLM 02. After fall 1942, with the exception of the wheel wells and flap areas, they were left unpainted. . Gun bay areas generally retained their RLM 02 paint. They exhibited the golden color of the Alcad skinning material. Aluminum and other alloy areas were still given a coat of RLM 02 to prevent corrosion. However, galvanized steel was left unpainted. Equipment such as guns, fuel tanks, oxygen bottles, etc. were in the color applied by the manufacturer. Guns were usually black or gray. Fuel tanks were usually black or gray. Oxygen bottles were usually overall blue, or painted with blue stripping.
Exceptions
Repaired areas were usually painted with whatever paint stocks were available, or left unpainted. Gun bays on late war aircraft were sometimes seen in natural metal.
Flap Areas
For aircraft with split or Fowler type flaps, the flap `well' and interior of the flap was painted with RLM 02. This is also true of the radiator flap and cowl flap areas.
Exceptions:
Bf-109B/C/D/E's usually had the underwing radiator area painted the same color as the fuselage underside. Some late war Fw-190's exhibited natural metal flap areas.
Wheel wells:
Now for the area you�ve been waiting for. Few regulations specific to the wheel well area exist, company and factories instructions usually deciding the matter. In keeping with standard practices as identified above, wheel wells and components should have been RLM 02. This includes tailwheel and nose wheel areas. Main gear and nosewheel struts were painted RLM 02, with the exception of the polished steel oleo area. Shock absorbers were a very dark gray, again with the exception of the polished steel telescopic sections. Cast and stamped wheel hubs were painted in semi-gloss black. Tailwheel hubs were usually unpainted (dark gray), or painted the underside color.