OK, here's an idea. Fill a milk jug full of paint. Maybe try to layer different 4-6 different colors. Put your paper a foot or so behind and above the milk jug. Shoot it with a 12 ga or whatever and see what kind of pattern you can throw on the paper.

I am NOT an artist, so it probably wouldn't work. I'll try to post a picture here of my son shooting a milkjug full of water. Don't know if I can get it to work from here, may have to wait until I get home tonight.

Here goes. Well, it didn't work the first time,, here goes again.

OK, I'll do it tonight.