In this activity (17th on the page), learners investigate why you cannot see colors in dim light. With five pieces of paper of different colors in front of them, learners sit in the dark for about 10 minutes. Then, they try to correctly label each piece of paper by color. After the lights are turned on, learners check for mistakes and compare with other learners. Use this activity to introduce learners to how photoreceptors, particularly rods and cones, in the eye work.