If you want multiple layers with sharp edges between them, you need to shoot the base color, let it dry, then cut masking for everything you want to be the base color. Shoot over that with color 2, let dry, mask everything you want to stay that color, etc. When you finish and peel the masks, you'll have a nice job with sharp edges.
If you want multiple colors with fuzzy blends between them, get a hobby airbrush. I can shoot about a 1/16" line with mine using low pressure and thin paint, working close to the object I'm painting (about an inch away). I actually like the airbrush soft edges better for a camo pattern, but the setup costs a bit and you need some practice to get it down (not a lot, a couple hours and you'll be able to pull off a gun camo job no sweat). /ubbthreads/images/graemlins/wink.gif
I found that camo hobby paint from the plastic model section of a good hobby shop is some very fine-pigmented, thin paint. Testor's ModelMaster paint shoots like a dream through an air brush when thinned with their thinner until it's like skim milk. I guarantee you can get a decent job using that, then shoot a matte clearcoat over the whole thing when you're done. Very flat finish.
They also make Polly Scale acrylics in camo colors, which a lot of people praise for painting plastics, but I had a harder time working with that. It seemed a lot tougher to shoot very small volumes without plugging the brush up, unless you thinned it so much it wanted to run.
You could do some amazing camo with the air brush if you planned it out first and took your time. /ubbthreads/images/graemlins/grinning-smiley-003.gif