What color were the Raiden’s wheel wells? I’m seeing the same grey as the underside and Atoke protective. But nothing seems definitive.
Hello,
I’d go for natural metal (no corrosion protection needed for a land base aircraft).
Internal landing gear cover panels may be light grey according to this picture 
J2M3
If you compare the inner central gear cover panel area on this A6M5 to the above Raiden picture you’ll see that it is much darker inside (Aotake).
Same with this A6M8 prototype, even if the picture is bad