There's botany behind the beauty
hen leaves transform in the fall, they're not so much changing color as they are revealing the colors that have been hiding there all along.
Trees use their leaves to collect sunlight, which gives them energy to create food for themselves out of water and carbon dioxide. That process takes place in cells containing chlorophyll, known for its bright green pigment. So, during the high-sunlight, prime food-making seasons of spring and summer, chlorophyll pretty much drowns out the other colors in the leaves.
But as hours of sunlight get shorter and nights get colder in the fall, the food-making process slows and the chlorophyll breaks down, giving the other colors a chance to show off. Aspens go golden, sugar maples turn orange, and dogwoods sport red and purple hues.
Weather-wise, the ideal conditions for fall color are clear days and cool--but not freezing--nights. An early frost will weaken colors, and a drought will kill off the leaves before the fall show has even started.