Here's some pics of a 6mm vehicle from Steel Crown Productions. I used a method I found on YouTube (from user trybeinganihilist), but instead of using an airbrush, I got brave and used cans of spray paint.
I have to say I am fairly amazed on how well it turned out. I used white tack to cover parts of the model while I applied a different color to achieve the two-tone camo look. As I do more, I'll refine the technique. Maybe I'll even get a new airbrush to use!