These new molecules are stored in other parts of the tree. With the green chlorophyll gone, the yellow and orange carotene pigments in the leaves can be seen. Carotene molecules don't break down as easily as chlorophyll molecules do, so they are present after the chlorophyll is gone. The same is true for the pigment anthocyanin , which is responsible for the red and purple colors in autumn leaves. The amount of anthocyanin and carotene in autumn leaves differs for different species of trees, and also for the same tree under different climatic conditions.
Cool temperatures increase the sugar content in leaves.
High sugar content in leaves and ample sunlight are conditions that favor the formation of anthocyanin. That's why, following a period of bright autumn days and cool nights, anthocyanins are formed, and the leaves are gloriously colored with red and purple hues. Clifford's First Autumn . For kids ages 4 to 8. Red Leaf, Yellow Leaf .