As the days get shorter and the nights get cooler, the chlorophyll in leaves starts to break down. Chlorophyll is what makes leaves green and helps them absorb sunlight for photosynthesis. Once the chlorophyll breaks down, other pigments in the leaf are revealed. These pigments include carotenoids (yellow and orange colors) and anthocyanins (red and purple colors). The amount of these other pigments varies from tree to tree, which is why some trees have brighter fall foliage than others.