Certainly lookin' a lot better KB73, but it still looks a bit like a paintbrush stain. Also, there are two things that leave a mark in the fuselage.
When a WW2 plane starts its engine, the exhaust fires up throwing up smoke in the air. This smoke itself is almost white, and does not leave a mark by itself.. but mixed with the smoke are very fine particles of oil, grime, and rest of the messy stuff which are a lot heavier than smoke. It's this sticky material that leaves behind the exhaust trails - and its effected by gravity.
The color itself is a mix of reddish brown and black - more prominent and defined with planes that doesn't get much regular maintenance. Planes with better regular maintenance will sometimes have only a very light shade of black as exhaust trails.
Notice how in the model, that the exhaust stains are dark black and brownish at the same time.. the shape is very naturally curved, following the lines of the upperwing, until it stretches back at the trailing edge.
To use one of my own works as an example, in the case of these 190As, they have broader exhaust ports. The staining material will fume out from the exhausts will leave a broader trail of stains that also follows the fuselage and will curve down a little bit.
A little attention to these small stuff can really make the plane look a lot better.
ps) Also, a closer shot to the fuselage reveals that the letter fonts for "12" could use something more defined. Check through the fonts of your graphics program and see if you have something that looks better.
