This is a project I have done with 6th and 7th graders and they love it. It's a fun way to decorate for springtime.
You will need paint cards (the free paint swatches from a hardware store). This works best with the tri-color cards, but if the card has four colors you could make it work, or cut off the fourth color. Usually I give about 7 cards to each group of students, but you can change this up to work however you need it to in your classroom.
Product includes directions for the students.