As I understand it the Japanese regs where much less specific then other countries. Interiors where "green". So what ended up happening was every manufacturer used their own version. Nakajima interior green is different then Mitsubishi interior green and on an on. Same applied to exterior colors. The one thing that is about as certain as anything though is that the Cockpits were not atoke.
If you really care about getting close to accuracy the white ensign colorcoats are thoroughly researched. Mr. Color also has nakajima and Mitsubishi specific colors.
But like these guys all said, if you are not super picky, Tamiya interior green is close enough. It was released to go with their 1/32 zero.
HTH
Mike