It is fall and we are waiting for the leaves to turn, be it maples at Fourth of July Campground, aspen at 7,000-9,000 feet, or cottonwoods in the bosque.
There are three different pigments in leaves, but the green of chlorophyl blocks the other two during the long growing season of summer. Once the days start getting shorter and the nights longer, the chlorophyl pigment decreases. Then the carotenoid yellow/orange comes forth. Anthocyanin is the red pigment found in the maples. This color is also related to the sugars trapped in leaves.
Ideally, a wet late summer with a drier frost-free fall produces the best color. Autumn color is affected by tree health. Drought and insect damage to trees cause leaves to fall sooner. Leaves begin to drop as their veins become clogged with dying cells.