Take the lid off of a shoe box, and cut the lid in half. Tape half of the lid into the shoe box using masking tape to separate it into two sections.
Set the shoe box upright onto a table that receives a lot of sunshine.
Place one plant on each side of the divider. Make sure that the plants are as similar as you can find. For example, you can select two plants that are the same type and size. Water the plants well before placing them into the box.
Tape the other half of the shoe box lid onto the front of the box, covering one of the plants completely. This will prevent one of the plants from receiving sunlight. When a plant does not receive sunlight, photosynthesis cannot occur and the plant will be unable to produce the chlorophyll that it needs to develop.
Leave the box undisturbed for one week. After a week, take off the lid to expose the plant that was hidden from sunlight. The hidden plant will be yellowed.