If you care about historical accuracy and you don't paint markings yourself but rely on decals, here's what's out there on the Mitsubishi Ki-51 "Sonia".
Let's start with the 44 Sentai.
The unit was organized in July 1939 with elements from the 3rd Daitai, 18 Dokuritsu Chutai and the 45 Sentai. In September 1940, the unit was reorganized, the 18 Dokuritsu Chutai was reassigned and the 17 Dokuritsu Chutai joined in. The unit came to be organized with the 1 chutai being equipped with "Sonia", and 3 chutai with Tachikawa Ki-36 "Ida".
During the Battle of Changsha, in 1942 the unit was equipped with one chutai with eight "Sonias" and two "Ida" chutai with five aircraft each. So, in general the unit never had many aircraft in its strength.
The 44 Sentai used a small hinomaru with a white surround as its tail marking and various combinations of fuselage bands and tail curved lines and bands indicating different shotai and personal aircraft. The following illustration by Nohara Shigeru featured in Maru Mechanic shows one such aircraft from the unit.
There are a few videos featuring 44 Sentai "Sonias".
The first one is dated September 1941 and shows 44 Sentai "Sonia" attacking supply barges and shipping on the Yangtze River.
Although not of the best quality, we can make out the unit marking, the band(s) on the fuselage and on the tail.
The aircraft below in the foreground seems to have no band on the tail and a white and possibly yellow band on the fuselage.
While this time the aircraft in the foreground has a white band on the fuselage and a curved red line on the tail. Note that all "Sonia" have the older shorter spinner.
Another video dated October 1941, features "Sonia" and "Ida" attacking enemy positions during the Battle of West Hubei.
The "Sonia" in the begining of the clip taking off, has a thick yellow band on the tail and a white band on the fuselage.
A third video of th unit can be seen in an older post, here.
A still shows two "Sonias" in the background, one with a red and a white band on the fuselage and a red band on the tail and the other with a red band on the tail and one white band on the fuselage.
There are a small number of very high quality photos featuring 44 Sentai "Sonias". Let's see some close-ups.
Probably yellow (or red) bands on the tail, one red band on the fuselage of the plane in the foreground, two red one white on the plane in the background.
Yellow and red band on the tail, but also notice the aikoku insrciption separating the white fuselage band.
In the photos below there are two different aircraft. One with a yellow and white band on the tail, the other with a red and white band. Note that none of the aircraft in the clips or in the photos have fuselage hinomaru.
Based on the above photos, and most probably not having access to the news clips, Akimoto-sensei proposed in Maru Mechanic that the cowlings of the above "Sonias" had this curious paint job. You can find artwork on the net showing 44 Sentai "Sonias" with such cowlings, sometimes in red or black.
He also asserted that the some top areas of the wings were in white. Here's a photo showing the darker areas on the cowling and the white wing as well as the artwork.
Here's a still showing two 60 Sentai "Sally" bombers with white on their wings. Notice how uneven the white areas are on the port and starboard wings.
In this case all the top surfaces of both wings look white, but not the front of the cowling.
Based on the evidence presented in the above clips, I believe that unfortunately the 44 Sentai "Sonias" did not have any wings painted white but sleet or ice or something similar has turned these wings areas to look white.
As we saw in the previous post, Wingsy and Hasegawa have provided kits and decals for 44 Sentai "Sonias" with the above schemes and recommend the wings to be painted white. I leave it to the modeller to decide.
Ofcourse all these hairyokushoku "Sonias" with the multi-color bands were gone when the unit started applying camouflage on their aircraft. Below is an example from Model Art #533.
The particular aircraft is the subject of the box art of the much older Hasegawa kit in 1/72.
Call me conservative, but I do not see any major differences in tonality. It looks to me that the same paint has been applied with only a small variation here and there, very common to all Japanese aircraft that had seen combat. At best, perhaps the areas around the cockpit where the rear machine gunner climbed into the cockpit or were more weathered, were repainted with fresh paint and as a result they look a bit darker. But nothing as dramatic as Hasegawa suggests in the instructions above. Interestingly the nose of the aircraft is very weathered...
...which I think supports my suggestion that the darker areas on the fuselage and tail are just patches of fresh paint.
There is also this classic photo with blothes, a model of which you can build by using the tail marking of the Rising Decals set for the above aircraft. Let's remember that "Sonias" left the Mitsubishi factories always in overall hairyokushoku; never unpainted like the Kawasaki "Hien".
Note also that all the cowlings have not been painted with dark anti-glare paint, even the aircraft in the photo above. I have seen "Sonia" models with black cowlings and, unfortunately, this detail is not correct.
