First, chlorophyll in the leaves starts to decline. Chlorophyll is constantly being made and replaced during the growing season and is responsible for the green color we see. As chlorophyll declines, we see the colors of carotenoids and tannins appear. These colors were always present in the leaves, but are not seen due the strong green color of chlorophyll. The carotenoids are responsible for the yellows and oranges that we see each fall.
Tannins cause the brown colors of some leaves.
With carotenoids and tannins are both present in leaves in the right combination, golden yellow leaves are the result. Anthocyanins are responsible for the pink, red and purple leaves. Anthocyanins are produced when sugars in the cells combine into complex sugars and are deposited in the leaves. The variety of pink, red, and purple colors is due to the various combinations of the compounds. This combination is influenced by the pH of the leaves, which is influenced by the soil the tree grows on.