If we assume the underneath of the cowl is light grey paint rather than bare metal the dark scratches and blotches on this area could be more dark green paint showing through an over-painted light grey coat. It is unusual to paint a light colour over the top of a dark one though and the scratches/blotches look too dark to be primer. Also the dark green areas of the cowl are heavily scratched showing the bare metal but there doesn't seem to be any similarly scratched bare metal areas on the light grey paint. It also seems odd the rivets are all uniformly darker on the light grey area. Perhaps one of our Japanese players could find out more regarding these Ki-61 parts?
My take on the engine cowl is this.
We have two colours on the external areas of the engine cowl in my opinion.
Looking at the external areas of the cowl I don't see any deep scratches that have penetrated to the bare metal at all. On the internal portions of the cowl we now have a third colour painted. When you look at the inside portions of the cowl there is a number of areas where the paint is missing. None of those bare metal areas on the back of the cowl look anything like the front portion of the cowling. They seem to match the bare metal areas of the spinner though. The spinner is of course dark green & you can see the brown looking primer in places.


I agree with you Greebo it would be strange to paint a light colour over a dark one.
I think that is what we have though.
When I zoom the rivets up large I see a light grey colour on all of them that matches the light grey areas surrounding them. Where the scratches have penetrated the light grey we have the same dark green again. The scratches on the sides on the green painted areas don't look to be deep enough to get to bare metal & look also to be light grey under the green. Also the green areas look to have some brush strokes where the demarcation line is on the light grey that are better seen on the second image down.


My best guess is we have one base coat of a green paint on all of the exterior of the cowl. Then a 2nd coat of light grey on all of the exterior of the cowling. Then a portion of hand painted third coat along the demarcation line on the sides of the cowling because they did not use tape.
Edit:
Here is a good shot of bare metal on the front portion of the cowl.
A line of rivets missing paint altogether except the one in the middle.
The middle one shows the light gray around its edges and its top has the green.

