Perhaps I'm wrong here (I have no painting experience), but I think you're overthinking this.
Let's see, I have this can of paint here, and I want it to make it look like a paint splatter on my rifle... What if you just.. splattered the paint? I'm pretty sure that will look as close to a paint splatter as possible, considering that's exactly what it would be.
If your going to use an airbrush or touch-up gun, you can splatter any paint or color you want.
Turn the material flow up and the air flow down. Different distances create different size drops or splatters...
If you are looking for the "webbing" type effect then you would be best off flinging paint off a brush or something similar. You can also try adding paint to a toothbrush and using a gloved finger to run over the bristles and splatter paint...try it first, you'll see what I mean.
Depending on the kind of paint you are using, I believe krylon makes a webbing spraypaint that is suppossed to give the same effect.
the krylon webbing works good.
comes in assorted colors.
you can buy at kraft supply stores(ask your wife) such as "Michaels", etc,.
or buy online, just google "webbing paints".
Black web over OD green works nice.
Black web over Tan or kaki looks good,
good luck and go for it.