Preparation for the activity (This can be done with the students if you have enough time):
Use painters tape to make random lines on the canvas or poster board. (Canvas works better than poster board when you remove the tape and stickers)
Add some star shaped stickers. ( I made the stickers a little less sticky by sticking them to a fuzzy piece of material first.)
My students used sponge brushes to paint on the red and blue paint. Their job was to completely cover the white. I added glitter to the paint for a little sparkle.
After the activity:
Let the paint dry completely, then carefully remove the tape and the stickers.