The leaves in my town are just starting to turn yellow, red, and brown. So this raises an annual question: Why do leaves change color? In the two-minute video below, ACS Reactions explains the chemistry:
For a longer explanation, here's a slightly silly (and wonderful) video from MIT's K-12 channel, spending much more time on the subject and including some chromatography experiments you can try at home. If you have nine minutes and/or kids, this is the video for you:
If you prefer your leaf-changing science in written form, check out Matt Soniak's article How & Why Do Leaves Change Color?