Those are called 'normals,' it gives the patches a texture that when hit by light makes them appear 3D in nature without actually being, well, 3D. There are tons of online generators online or you can use GIMP like I do with a normal map generator, although I forgot where I got mine so you'll have to do a bit of searching either way.
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theres a patch marines normally have in the middle of their carriers that would be cool to have for larp purposes, looks something like this