Apropos a recent interesting discussion over at j-aircraft.com about the colour of the licence built DB601 engine in the 'San shiki sen' (Kawasaki Type 3 Fighter Hien 'Tony').
Some suggested gloss black and the Fine Molds 1/72nd scale kits call out flat black (GSI C-33/H-12) but whatever the colour is in these photographs it does not appear to be black.
The remnants of paint on the extant Atsuta built example are a mid-toned slightly metallic looking bronze green, a colour I have seen associated with Ki-44 wheel wells and undercarriage covers. Could the Kawasaki engine have been painted the same greenish tan as the interiors of some Ki-61 aircraft, believed to be JAAF # 30 Karekusa iro (Dried or Parched Grass Colour)?
Image credit: © Bulletins Techniques de l'Aviation Japonaise 1925-1945 - Tetsuya Takeda & Junko Takamori