The leaves of trees change color in the fall because the tree is no longer producing chlorophyll, which is what gives leaves their green color. The green color of chlorophyll is due to the presence of a pigment called chlorophyll a. Chlorophyll a is essential for photosynthesis, which is how plants convert sunlight into energy. In the fall, the days get shorter and there is less sunlight available for photosynthesis. As a result, trees stop producing chlorophyll and the green color fades from their leaves. The other pigments in the leaves, such as carotene and anthocyanin, become more visible as the chlorophyll fades. The different colors of fall leaves are due to the varying amounts of these pigments present in the leaves of different tree species.