I do this often. I'll hit the GoodWill and find khaki's or use cotton camo that's faded and lost it's contrast. I use stenciled patterns I've cut from card stock and black exterior spray paint. When it's dried, I'll wash them and the stark color fades to a mute black.
I'll do this before turkey season if a pair needs it. By the time deer season rolls around, they've been washed several times don't smell at all.
The pic isn't great, but I have a pair on here, and have touched up my hat: