Since I was working from a file with each colour as a seperate layer, and not quite 100% opacity, I was able to do something a little more subtle than just adding some grey to the colour mix. The brighter spots are, I'm pretty sure, from the lighting.

Starkdog, I have that plugin. While it's good, it isn't going to give you anything much like any real military camouflage. For one thing, military patterns can have quite distinctive shapes to the blotches. Even with simil;ar colours, or a greyscale image, you can see a difference.

And the current pattern for the USMC is a whole different game.