To be completely honest, I'm really not sure where this idea came from originally. I've wanted to do this for a while, but didn't want to go buy tissue paper just for this. I wound up with several different colors of tissue paper on hand after a baby shower, and decided it was time to give it a go.
I started by taping a piece of contact paper (sticky side out) to a window, and cutting up several colors of tissue paper into small pieces. I didn't give Erik any instruction, but by now he's pretty familiar with contact paper and he jumped right in.