Massimo,
as far as i know, there is no additional information about this picture. It was sold on ebay some time ago, Jim posted it, i rightclick-saved it. The sentai emblem is probably white, but the quality of the image is so bad, that any speculation regarding the colors (which go further than "dark" and "light") would be futile.
More so, even the base color could just be guessed, as there are so few pictures of Ki-44s painted in a single color that i'd guess they left the factory always in NMF and were camouflaged in the field with more or less care. Even the Ki-44s that do wear a solid color show quite heavy chipping (real chipping, not left out or repaired areas!), which indicates a field-applied camouflage without a base coat. The grey-green Aomidori-Iro (~FS 34036, but it faded to some kind of blue-gray very soon) was a color that seemed to have been in widespread use on japanese fighters in the chinese theater. But that's just one possibility, it could also be lilac..
However, it seems that the hinomarus on the Ki-44 in our picture were not painted over before the application of the chinese roundels, because if the new owners had done so, they most likely would have overpainted the chipped area next to the hinomaru, too. It is also noticable that the strange fashion of applying the new roundel so out of place was repeated on the wing uppersurfaces (You can see the shine of the glossy hinomaru red next to the chinese roundel; at least in my opinion). Maybe the Shoki wasn't flyable at all (one of the prop blades is bent) and the Chinese marked them just for propagandistic purposes, for fun, painter training, out of boredom or anything else.
Finally, there is some sort of canvas hanging over the rudder, it is not paint chipping.
P.S. I just figured out that the plane on the picture we're talking about isn't a Ki-44, it's a Ki-84! In this case we have a Ki-84 factory finished in Aomidori-Iro or Ohryoku 7 ("late war brown"). So much for expert talk!
P.P.S. While looking for Ki-44s in a single colour i found a few more pictures for you, enjoy:
Note to myself: First look a the thing, then speculate about it!