Hi again,
There is an excellent cockpit walkaround in Replic n°200 with photos taken in 2002 of the NASM's Ki-45 in it's original colors. The interior color is really Dark Green (FS34083 is given in the accompanying article). But as I've said, there were variations. It seems the mid-production aircraft had this green color but maybe not the others. I'm not a specialist though...
For information, Hasegawa have specified a color mix based on Khaki in the instructions of both Ki-45 Kai Koh Toryu (09781) and Ki-45 Kai Tei Toryu (19195) kits. I don't have the third boxing of the kit.
Jean-Luc