Here's a curious idea: The red color in fall leaves is sunscreen.
A newly developed theory has come out about what causes fall leaves to turn deep red. The idea is that the red pigments, called anthocyanins, act like sunscreen.
During fall, trees break down and reabsorb as many nutrients from their leaves as possible before they fall. It's just as this reabsorption process begins that leaves begin producing high quantities of these red pigments. The idea is that the pigment protects the ultra sensitive photosynthetic tissues that generate the energy to drive this process of reabsorption.
This theory makes sense of a lot of yet to be explained facts about the coloring of autumn leaves. Like why there are more red leaves when fall consists of a lot of bright, sunny days. And why there are more red leaves when there are other stressors like near-freezing temperatures and drought. And why the outer leaves of maples are more colorful than the shaded leaves inside the canopy. Still, further research needs to be completed before we can validate this theory.