I assume you mean for the IL-2 series?
IL-2 has no reflectionmaps like this: http://www.simmerspaintshop.com/foru...tion-maps.html
So, you have to fake things.
You cannot make things glossier then they are.
At best you can "help" a bit with highlights and shades.
But a fact is that bright colors appear glossier then dark colors. So you can try to make a color a bit brighter to have it appear glossier.
To make things dull, the best trick it to use noise. Due to the noise you have no solid color than can look shiny like a solid color does.