There are several photos of this a/c with the same man in the cockpit. He's obviously not a pilot and the photos are from the Yokota Air Base, probably after the end of the war.The mottling effect is either surface corrosion of the steel skin or a very thin application of a camouflage paint INHG
View attachment 876077
Below another photo with the same a/c and US service men (those are not USAAF/USAF uniforms). IMHO it's natural weathering.
Source: Nakajima Ki-115 | World War Photos