Over the Rainbow
ooh fun! : SCIENCE FAIR PROJECT. This would be very easy for kids to participate in. Just buy white carnations and add food coloring to the water in the tubes and watch the flowers change color. this would be very easy for high school and middle school kids. However, with elementary kids you risk them making a big mess if they were to spill the water while handling the tubes.
Rainbow letter name photo
Draw on sandpaper and iron it on a tshirt!
SweeterThanSweets: Rainbow Ice - Tutorial