IL-2 makes especially bright colors look glossy.
I think that is also a reason why weathering is so popular in the IL-2 scene.
First, you can make the colors a bit darker.
Then use a noise layer to make the paint a bit less glossy.
Especially in the past I often used a grey layer for that. I've seen others do something similar.
Download one of my templates, and you will find that layer in it. Play with it's blending options (in top of the layers window). Often Multiply works, sometimes another gives better result. Also play with it's transparency.
It will darken the skin a bit, but it's the effect in game that counts.
A little tip for thepaint edges between the dark and light grey: Use a brush instead of a pencil. That will give much more fluent edges.
For hard horizontal and vertical lines the pencil is best, in almost any other case the brush is better.