The sugars react to the sunlight and to the cooler weather by turning bright colors. The Best and the Brightest. All leaves change color before they fall from the tree. But some leaves are more colorful than others. Just as some people's hair changes as they get older, some leaves can only change to yellow or green.
Weather conditions are another factor that affects the color of fall leaves.
The best and the brightest colors occur in years that have wet summers, cool fall nights, and warm sunny fall days. In Illinois, the best and the brightest fall trees are hard maples, red oaks, ash trees, sweet gum trees, and sassafras trees. At the beginning of the school year have each student bring in a leaf from the tree of his or her choice. Have students press the leaves between newspaper sheets and then mount them on a piece of paper, preferably under clear adhesive plastic, leaving room for a companion leaf. In the fall, after the leaves have changed, have each student bring in a leaf from the same tree.