DENVER (KDVR) — Colorado has some of the best places in the country for fall colors, and arborists expect it to be a more vibrant-than-average foliage season. You’ll see shades of red, purple, orange, yellow and gold, depending on the tree.

Not all trees change color or even shed foliage, but for those that do, there is a science behind it. Ever wondered why all of the aspen trees shift from bright green to a bright golden yellow?

Colors change depending on several factors including tree species, health, weather, elevation and environmental factors.

Chemistry of changing colors

Like any color palette, leaf colors depend on pigments. According to the Forest Service, there are three pigment types responsible for the autumn colors.

Chlorophyll is what gives leaves their green color via photosynthesis. In other words, chlorophyll is what allows plants to use sunlight to produce sugars and foods. Its continual synthesizing throughout the summer requires sunlight and warmth.

As days get shorter and nights get longer, biochemical processes begin. Chlorophyll regeneration slows down and eventually diminishes, allowing other pigments, carotenoids and anthocyanin, to show their colors.

Carotenoids are present in leaves throughout the growing season, but once the chlorophyll breaks down, carotenoids bring yellow, orange and brown colors to the spotlight. Carotenoids are also what make corn and bananas yellow, and carrots orange.

Anthocyanins are produced as the seasons change in response to bright light and excess plant sugars in the leaves. When sugar concentration is high, anthocyanins dissolve in the cell sap. Bright red colors are a result of cell sap being more acidic. But if the sap is less acidic, the color is more purple.

How does the weather affect fall colors?

Temperatures and moisture levels that occur before and during the time that chlorophyll is dwindling are the main influencers.

Yellow colors are fairly consistent from year to year, according to the Forest Service, because carotenoids are always present in leaves. But the red colors vary more.

A wet and warm growing season, followed by a sunny autumn with cool nights results in the brightest fall colors, according to the Forest Service. During those days, sugars are produced in the leaves, but the cool nights cause veins in the leaf to close. So sugars are essentially trapped in the leaf, spurring the production of anthocyanin pigments and shades of red.

Colorado is considered a prime color region because of the right combination of tree species and likely weather conditions.

Which trees turn which colors?

Deciduous trees, or trees that drop leaves and remain bare until they grow new leaves in the spring, are the trees that change colors.

Pines, spruces, cedars, firs and other evergreen trees are able to resist freezing, and thus remain green through most winters. Needles do fall eventually because of old age.

Different tree species display fall colors at varying times, and some exhibit little color other than brown as the leaves shrivel up and fall.

The U.S. Forest Service lists colors that are characteristic of particular species:

  • Oaks: red, brown, or russet
  • Hickories: golden bronze
  • Aspen and yellow-poplar: golden yellow
  • Dogwood: purplish red
  • Beech: light tan
  • Sourwood and black tupelo: crimson
  • Red maple: brilliant scarlet
  • Sugar maple: orange-red
  • Black maple: glowing yellow
  • Striped maple: almost colorless

Some trees will display both yellow and red. Those leaves change to bright yellow as chlorophyll disappears, and then turn red as sugar concentration increases.

Ultimate Fall Guide 2023

Fall colors, events, things to do in Denver

Check out more of the fall guide

FOX31’s Pinpoint Weather team has created a fall colors forecast and map of when and where to see peak colors based on local conditions.

If you get the chance to go leaf-peeping, FOX31 wants to share your photos online and on air, submit photos here.