I did mine by using home made "stickers". Take a sheet of wax paper about two feet long and cover both sides with blue painters tape. Draw various sizes random squiggles, dots, and the like then cut them out with scissors. You now have two sets of stickers. I found where I wanted the "white dots" and painted those areas. Wait 24hrs to dry and apply the stickers where you want the white. Then add your next color, let dry and layer up again. Keep layering and painting and by the end of the week, take off all the stickers and you should have a nice camo job.
Prep is key here unless you don't mind some flaking since it may not have fully attached to an unprepared surface. If you plan on swapping colors around, then lack of prep my be a plus.