Leaves have chlorophyll in them that give them green pigment during the warmer months. In the fall, when the temperatures get cooler and the sun angle changes, the tree’s chlorophyll starts to break down.
Eventually, the green color disappears and other colors become visible. The leaf color depends on the pigment present in the leaf.
Yellow leaves contain xanthophyll, orange leaves contain carotene and red leaves contain anthocyanin.
When fall brings dry days with cool nights, the colors of the leaves appear brighter.
Fall colors are just starting to peak in some of Colorado’s mountains. The colors will peak first in the northern mountains and last farther south.
The southern mountains will see peak colors toward the end of September into the first month of October.