Hello,
I made some researches for my Ki-61- I Ko project; there is some probability that for the early series, the cockpit color was in #3 "Ash Indigo" (hairanshoku) blue-grey, the same as Ki-21 or Ki-27. This color was officially specified by IJAAF for cockpit color since 1936. But it seems there is some modification from 1943 and the cockpit color was painted in #29 "Yellow Green" (Ki Midori Iro), similar to so called Nakajima cockpit interior. Other point, not all the IJAAF fighters were in this cockpit color, it seems that Ki-43-Is were in aotake cockpit color...