Pictures of actual uniforms in a museum on a Belgian uniform website show a very dark blue uniform, a Prussian or Navy blue. In order to show a bit of wear and contrast in the folds I'm going to use a Prussian blue craft paint, thinned just a little so that the outer creases come out slightly lighter (over a white or light grey primer). If that doesn't come out right then I'll try again with less thinning or try a darker blue. The Foundry pictures are probably a bit too light a shade of blue.