Krylon Fusion, it's great on plastic. Krylon Marbelizing for the webbing, search for it on Amazon.
Remove pistol grip cap, kick pad, butt plate, etc...all the components you don't want paint on.
For plastic, rough it up with sand paper. For wood, get it down to as close to bare wood as possible.
Wipe off with a damp sponge or cloth.
Mask off action area and barrel channel, and anything else you don't want paint on. Use blue painters tape. Take your time and do a very thorough job, cutting with a razor knife where necessary.
Hang by a wire, in an area where it can stay for a few days.
Spray the first coat, light. You'll be doing three to four coats, so make them light. You shouldn't start to get full coverage until the third coat.
Give it 3-4 hours between coats. This part is key, the curing time will pay off.
After the last coat, let it dry 24 hours, a few days would be ideal.
Holding marbleizing spray a foot away from a piece of cardboard, practice a few strokes. This will be a 3-4 second sweeping spray. It comes out in very thin ribbons of paint. A few practice passes will really help.
Spray the marbleizing spray in a complete pass from end to end, both sides. Don't touch it for a few hours.
Let is set up a few days and decide if you want to use clear coat or not. I've done both. It will change the colors, slightly. Order the marbleizing from Amazon. Its a small can, enough to do several guns.