Truekill skin looks good. Majority of the details folks see/look for are as follows: Panel line width/brightness, rivet width/brightness, pixelated areas, natural surface textures (cloth style/metal style) and weathering that has too much or too little noise in it (variation of opacity, color, and fading).
By the last one when I say noise smoke and dirt will fade obviously more in some areas than in others. Each type of build up will also have a different color variation to it. Smoke coming from guns will typically have a grayish black tint with fading on the sides coming to a tip at the end. Exhaust smoke can be a blcakish grey also with a hint of brown or to it. Best thing to do is find some decent photos with that type of bird and compare between a few to see common areas that collect these different dirt and smoke.
The P-51D has a really distinctive area between the flaps and ailerons that tends to collect dirt and grime. In the end it seems to show three distinctive spots of wear. One at the absolute corner of the ailerons/flaps and then one on each side of the flaps upper and outboard areas. These three areas are only about 6 inches or so apart. If you connected the dots they'd make an almost perfect triangle. It also has distinctive areas along the trim tabs on both the ailerons and horizontal stabs where the control rods are.
These are just some things to keep in mind. The more detail the better in some cases. Paint jobs aren't always perfect. They have overspray, multiple layers of paint and some areas are more prone to weathering than others not only in the sense of faded paint but chipped and weathered paint.
