Leaf Colors Explained: Green, Yellow, …Blue?


Fall color has peaked in the Roaring Fork Valley! Enjoy the amazing views!

You may know that Aspen leaves (and most plants) are green throughout the growing season due to chlorophyll, which enables plants to convert light from the sun into usable energy. In order to survive the harsh temperatures of winter, some trees enter a dormant state. When they stop producing chlorophyll, the base colors of their leaves are revealed. In the case of Aspens, the leaves turn a beautiful golden yellow!

What you may not have considered (and now should) is the more basic question…why is chlorophyll green? Why not some other color? The reason is our sun! Based on the amounts of different colors of light that radiate from the sun, it is most efficient for plants to reflect green light. If they absorbed all light it would be too much, and if they reflected more light they wouldn’t get enough. Since they reflect green light, that’s what we see – and that’s why almost all plants that have survived the process of evolution on Earth are green.

Wait – yes, I intentionally specified Earth. Then what about other planets??? Alien plants could be different colors. If a planet orbits a very high energy star, plants that grow on it would likely need to reflect high energy light so they don’t get scorched – they would be purple! Plants getting light from a low energy star would likely need to absorb all of the energy they can – so they would be black! And everything in between. So while we are treated to trees with yellow leaves in the Fall here…there may very well be a forest out there somewhere full of leaves that grow naturally bright blue!

Here is a bit more info and some artists’ representation of what these plants might look like, if you are interested!

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