The best photo I can find is of a Ki-84 on a carrier deck being shipped to the States post-war, it appears the interior surface of the inboard wheel cover is natural aluminum with darker framing. A picture of the airplane in Kyoto makes it appear that the gear well was either aluminum or white in that restoration. In all the wartime photos I could find, the lighting is so poor that the inside of the gear doors appears black, but I doubt they were. I also doubt they were Aotake ( the metallic blue-green). Don't think you could go wrong with aluminum.