Discuss “Where’s the green?”

As nature bursts into color this autumn, chemical processes transform leaves, and leaf peepers hike through mountains in pursuit of nature’s deepest hues.

In autumn, large changes come in small sizes.

Frederick Utech, adjunct professor of biological sciences, said that when temperatures drop, autumn leaves form an abscission zone, or a collection of tightly grouped cells within the leaf. As this happens, the leaf’s chlorophyll molecules break down and other pigments show through.

Leaves contain several color pigments, the most dominant of which is chlorophyll, the green pigment that is responsible for photosynthesis. When the chlorophyll breaks down, it produces magnesium, which goes back into the tree to make chlorophyll for next...