First the students take their paper and glue down pre-cut squares of red, yellow, and blue (primary!!!). We discuss how it's okay to overlap the squares! The students really had to concentrate on keeping the squares/rectangles as squares and rectangles instead of turning them on their side and making them into diamonds. They also had to work on keeping the squares within the boundaries of their paper.
Lastly, we added black lines by dipping pieces of cardboard into black paint. I really had them focus on going slow and steady so that they didn't get paint everywhere (i.e. if the cardboard is the only that is touching the paint then they "shouldn't" get paint on their hands and on the table. This helps cut down on mess!). We talked about vertical and horizontal lines and how to make these lines on our papers with the cardboard and paint. We really focused on "pressing" the cardboard onto the paper instead of running the cardboard across the paper like a paint brush.