Why Do Leaves Turn Colors in the Fall?
The green we see in leaves all summer comes from the green pigment “chlorophyll,” which leaves use in making food. Other colors – red, orange, yellow, and purple – are present in the leaves, too.
But during the spring and summer, the leaves have so much chlorophyll that we usually cannot see the other colors. In early autumn, before cold weather sets in, many trees stop making food. At the same time, the chlorophyll disappears from the leaves.
The decomposition rate of chlorophyll remains constant, so the green color starts to fade from leaves. The reds, yellows, and other autumn colors that had been covered up by the green of chlorophyll then become visible.
However, it’s mainly light levels that are responsible for fall foliage colors. Sunny autumn days are needed for the brightest color displays, since overcast days will lead to more yellows and browns.