The Miracle of Fall
is on the website of the University of Illinois Extension Service. This is an informative set of web pages including why leaves change color in the fall, where to see the best fall color (traveling) and a list of trees that have exceptional fall foliage colors, among other sections of the website. Each section also has links for further information. A pretty good general site if you want to learn more about Autumn Colors.
Below is an amazing diagram revealing the structure of a leaf. The diagram is from the Missouri Department of Conservation online. You can see the carotenoids and anthocyanins hidden in the leaf's cells, waiting for the chlorophyll to diminish so they can show off. Check out their fall color website here.