this is purely off the cuff
If  you live in the US, you can find numerous shades of dark blue acrylic paint at your local Michael's or other arts & crafts emporium, in two ounce bottles for around $1, and less when on sale

my preference is for Americana or Folk-Art or Delta Ceramcoat
these three brands probably have a half dozen shades which would work,
from an extraordinarily dark blue like a just-issued uniform, to a more washed out shade that still is dark blue
which would be entirely appropriate for campaign-type dress, in light of inconsistent dyestuffs and the effect of weather on uniforms

I'd probably go for the Americana Midnight Blue, and then highlight it with a little random drybrushing in a yet lighter shade, perhaps a dark royal blue
the Americana Prussian Blue is too dark for my tastes

Americana does publish a chart showing which of their colors are appropriate to highlight and shade a particular color, I can forward that info if you wish

ultimately, you need to feel happy about how the troops look

Michael Montemarano