Why Do Leaves Change Color in Fall? The Pigments Behind Autumn Color

As an Amazon Associate we earn from qualifying purchases.

Why do leaves change color in fall? Because the green pigment in them fades, and pigments already present in the leaf become visible. The National Park Service explains the starting point: “Each leaf contains a pigment called chlorophyll.” This guide explains why leaves change color in fall, which pigments produce each color, and what affects how bright the display is, using two sources.

Quick answer

• Chlorophyll breaks down in autumn. The National Park Service says that “As autumn progresses, a tree will send a substance to each leaf called an enzyme that is directed to take apart chlorophyll pigments.”
• Once chlorophyll is gone, other pigments show. The National Park Service says that “Once the chlorophyll breaks down, the other pigments that weren’t visible to the human eye before are now on full display!”
• Yellow and orange come from carotenoids, and red and purple come from anthocyanins, according to the Illinois Extension article.
• Weather changes how bright the colors are. The Illinois article says that “Windy, rainy fall weather is not your friend since these conditions tend to knock leaves down before they’re ready to give their full display of color.”

Why the green fades first

Chlorophyll is the pigment that does the work of capturing light for the plant. The National Park Service states that “Chlorophyll is also what gives a plant its green color.”

The Illinois Extension article describes the role of chlorophyll more fully. It says that “In the growing season carotenoids and chlorophyll work together to absorb visible light energy, which is converted to chemical energy through photosynthesis.” In the fall, the same article says, “chlorophyll breaks down more quickly, revealing the yellow and orange of the carotenoids as these pigments continue to process energy for the resorption process.”

The Illinois article describes the process this way: “Senescence is the process of leaves’ breaking down complex molecules into smaller soluble ones, such as sugars and amino acids.” It adds that “Resorption of the sugars and amino acids allows the tree to recover energy that would otherwise be lost when the tree sheds its leaves at the end of senescence.”

What the tree does with the nutrients

The National Park Service describes the step that comes after the green fades. “Once the chlorophyll has been broken down, the tree will take the last of the nutrients left in the leaves and absorb it back into the branches and trunk before each leaf falls to the ground.”

The Illinois article explains why chlorophyll still matters at the end. “It takes energy for the tree leaves to resorb those soluble compounds back into the tree, which means the chlorophyll still has a job to do in producing this energy.” Once chlorophyll is gone, the leaf is exposed. The article notes that “But with chlorophyll quickly degrading, the leaf is now vulnerable to ultraviolet exposure from sunlight, pests that might take advantage of a dying leaf, and a host of other environmental factors, including freezing temperatures.”

Which pigments make which colors

The two sources name the main groups of pigments.

Yellow and orange: carotenoids

The Illinois article says, “The orange and yellow colors you see in the fall are carotenoids.” It also notes that “They are present throughout the growing season, but chlorophyll’s green pigment is so overpowering that our eyes can’t see the others.” The National Park Service gives an example: “A good example of this is carotene, the pigment responsible for orange leaves.” The article adds, “It is the same pigment that makes a carrot orange!”

Brown and copper: tannins

The Illinois article says, “Tannins cause the autumn browns and coppers seen in fall” in oaks and beech trees. It also describes tannins as “considered a waste product of certain plant processes.” The article says this pigment “is also present throughout the year, but it is visible only after the chlorophyll fades.”

Red, purple and crimson: anthocyanins

The Illinois article identifies the source of the reds directly: “The brilliant shades of red, purple, and crimson come from anthocyanin.” It explains how they form: “Anthocyanin forms as plant sugars accumulate in the leaves because of the ever-constricting abscission layer, which slowly narrows the tubes that allow the tree to resorb nutrients.”

Light affects how red a leaf gets, according to the same article. “The more sunlight a leaf is exposed to, the more sugar is produced; the more sugars that accumulate in the leaf, the more anthocyanins are produced, and the redder the leaf becomes.”

Why some autumns look brighter than others

The National Park Service says that “The temperature and rainfall can affect the brightness of the fall colors.” It gives a direct example: “When there is a cool fall, the red maple leaves appear brighter as well.” It also notes that “When there is more rain, the colors pop even more!”

The Illinois article says that yellow and orange colors are more predictable than red. In its words, “Yellows, golds, oranges, and even browns are fairly consistent from year to year, but anthocyanin can be unreliable.”

The article also makes a point about weather. “Windy, rainy fall weather is not your friend since these conditions tend to knock leaves down before they’re ready to give their full display of color.”

Why the pigments differ between trees

The National Park Service explains that “Every tree has a different combination of pigments remaining which gives leaves their unique colors.”

The Illinois article adds that “Not all plants are genetically programmed to produce anthocyanins, but some produce reddish foliage all year long, including the well-known Crimson King Norway Maple.”

What the sources say about the purpose of color

Both sources explain that leaf color is linked to the tree’s processes, not only to appearance. The Illinois article says that “Anthocyanins perform a multitude of functions in fall, including absorbing free radicals and protecting plant leaves as they move nutrients back into the tree.” The same article reports a theory that “the anthocyanins’ red color warns leaf-feeding insects to stay away,” and it presents this as a theory, not a settled fact.

What we could not verify

The two sources explain the mechanism well, but they do not answer every question about fall color. The gaps are listed below.

What the sources do not say

• The sources do not give a date for when leaves change in a given region, so this guide does not suggest one.
• The Illinois article presents the insect-warning idea as a theory, and the sources do not confirm it.
• The sources do not explain why some trees produce more anthocyanin than others beyond the sugar and sunlight relationship quoted above.

How we chose these sources

Both sources are public pages that explain the science in plain language. The National Park Service page is a federal source, and the Illinois page is a university extension article. Both returned HTTP status 200 when checked on 2026-10-27. Every quote in this guide is copied from the text of those fetched pages.

Frequently asked questions

Why do leaves change color in fall?

The National Park Service says that “As autumn progresses, a tree will send a substance to each leaf called an enzyme that is directed to take apart chlorophyll pigments.” Once chlorophyll breaks down, “the other pigments that weren’t visible to the human eye before are now on full display.”

Which pigment makes leaves orange?

The National Park Service says that “A good example of this is carotene, the pigment responsible for orange leaves.” The Illinois article says that “The orange and yellow colors you see in the fall are carotenoids.”

What makes leaves red in fall?

The Illinois article says that “The brilliant shades of red, purple, and crimson come from anthocyanin.” It adds that “The more sunlight a leaf is exposed to, the more sugar is produced.”

Does weather change fall color?

Yes. The National Park Service says that “The temperature and rainfall can affect the brightness of the fall colors.” The Illinois article adds that “Windy, rainy fall weather is not your friend.”

Why do some trees turn brown instead of red?

The Illinois article says that “Tannins cause the autumn browns and coppers seen in fall” in oaks and beech trees. The sources do not give a full explanation of why a given tree produces tannins or anthocyanins, so this guide does not go further.

For what to do with fallen leaves after they drop, see how to make leaf mold at home. For fall planting plans, see how to plan a fall garden.

Sources

• National Park Service, Why Do Leaves Change in the Fall? https://www.nps.gov/articles/why-do-leaves-change-in-the-fall.htm (HTTP 200, checked 2026-10-27)
• University of Illinois Extension, Good Growing blog, 2019-10-08, Why do tree leaves change color in autumn? https://extension.illinois.edu/blogs/good-growing/2019-10-08-why-do-tree-leaves-change-color-autumn (HTTP 200, checked 2026-10-27)