Why Do Leaves Change Color in Autumn? The Pigments That Were Hidden All Summer

Many trees in cooler regions turn from green to yellow, orange or red in autumn. The colors are not painted on at the last minute. Some of them were in the leaf all along.

Three pigments

The US Forest Service lists three leaf pigments involved in autumn color:

• Chlorophyll gives leaves their basic green color. It is needed for photosynthesis, the process plants use to make sugars from sunlight. Trees in temperate zones store these sugars for the winter dormant period.
• Carotenoids produce yellow, orange and brown colors. They are also found in things like carrots, corn and bananas.
• Anthocyanins give color to things like cranberries, red apples and blueberries. They are water soluble and appear in the watery liquid of leaf cells.

Why green fades

During the growing season, the Forest Service explains, chlorophyll is continually produced and broken down, so leaves look green. As nights grow longer in autumn, chlorophyll production slows and then stops, and eventually all the chlorophyll is destroyed. Carotenoids and anthocyanins already in the leaf are then unmasked and show their colors.

Both chlorophyll and carotenoids are present in leaf cells through the growing season. Most anthocyanins are different: the Forest Service says they are produced in autumn, in response to bright light and excess plant sugars in the leaf cells.

What sets the timing

The Forest Service says three factors influence autumn color: leaf pigments, length of night and weather. The timing of color change and of leaves falling is primarily regulated by the calendar, as nights become longer. It notes that other influences, such as temperature, rainfall and food supply, are not as unvarying as the steady lengthening of nights.

What is still not fully known

The Forest Service is open about the limits: scientists have worked for years to understand these changes and, although not all the details are known, enough is understood to explain the basics. Weather can change how bright a particular year looks, but the underlying cause is the same each autumn.

Sources

• US Forest Service, Science of Fall Colors: https://www.fs.usda.gov/visit/fall-colors/science-of-fall-colors

Facts checked: October 9, 2026.