We used an old plastic ice cream tub, but it works just as well with a shoe box or any kind of box with a lid. Then we placed a piece of paper in the box, added some dabs of paint and dropped in the marble. We slowly rolled it around with the lid off to see what was happening. Then we put the lid on and shook it faster. We made five pictures, each with a different combination of colors (red, yellow, blue, white, black). A's favorite was the one with all five colors. Oh, and the all blue one is mine....what can I say? I wanted to get in on the fun too!
I tried to make purple for him, but it came out too watery. I grabbed a straw and let him blow it around in the box to make a different abstract design. He concentrated very hard on this, but in the end preferred the marble approach.
Considering the mess was negligible and the fun was substantial, we are going to pull out this activity again soon. And I'm so glad it gave me an opportunity to finally contribute to Unplugged!