Couple ways of doing it, would you be using krylon/spray cans or an airbrush?
If using spray cans (less control) shoot a base color of tan and tear out some patterns of blue painters tape and put those where you want tan spots, leave the tape until your done. Next hit the entire thing with black and repeat tearing out tape and putting it where you want black. Now leaving all the tape in place hit it with a final coat of green and peel all the tape off. That will leave your with a base color of green with tan and black spots.
On this one I did it in reverse with an airbrush, base coat was coyote brown, then black highlights, then tan over netting. The skull and crossbones were done last using a female stencil I cut out.