Without fresh water to renew it, chlorophyll begins to disappear. Other colors, which have been there all along then become visible. They are common pigments, also found in flowers, and foods like carrots, bananas and egg yolks. We do not know their exact role in leaves, but scientists think they may be involved somehow in photosynthesis. In the leaves, these pigments are formed in the autumn from trapped glucose.
Brown colors come from tannin, a bitter waste product.
Different combinations of these pigments give us a wide range of colors each fall. As the bottom cells in the separation layer form a seal between leaf and tree, the cells in the top of the separation layer begin to disintegrate. They form a tear-line, and eventually the leaf is blown away or simply falls from the tree. One more important question remains. The best place in the world for viewing fall colors is probably the Eastern United States.