Why Does Color Blue Hardly Occur Naturally?

black naped monarch
Black naped monarch (c) freepik.com

Blue is a very prominent color. But why only very few plants have blue and far less in Animals? Let’s try to explain it in simple.

First, let’s understand the Spectrum of Natural Light.

wavelengths of the visual light spectrum

The Blue color region of the light spectrum has a short wavelength with high energy. Therefore those are the waves absorbed by plants from the natural light mainly for photosynthesis. (Not gonna go into detail about photosynthesis here)

That’s why you would rarely see plants with blue leaves. In simple, colors you see on anything under natural light are the colors reflected by that surface absorbing the rest of the colors. Hence you don’t see Blue being reflected by the leaves.

Then how are there certain plants that do have blue flowers?

Most plants create the color blue by mixing up naturally occurring pigments (by varying the acidity).
That’s how plants like Hydrangea and Morning glory would create blue-colored flowers.

Now, what about animals?

Animals may appear in the color Blue for many reasons including, to attract the opposite sex during the courtship or more importantly to warn about their toxicity (aposematism) like the Blue Poison Dart Frog.

© Quartl. Blue Poison Dart Frog (Dendrobates azureus) in the Frankfurt Zoo, Germany.

But would you believe non of these animals including your favorite emoji butterfly (Blue Morpho Butterfly) are not really Blue but rather an optical illusion?

Usually, the pigments on animals come from the food they eat. For example, flamingos get their pink color from the tiny crustaceans they eat. But due to the lack of natural blue food, animals would not create blue pigmentation on them.

Going back to blue morpho butterflies, (or Blue tigers which are commonly found in Sri Lanka) they make the blue color from the scales on their wings shaped in a way that only the wavelength of blue light is reflected.

If their scaled were shaped differently, the color blue will vanish.

Then what about the birds?

Purple Swamp Hen (Porphyrio porphyrio) (Kithala කිතලා)

Similar to butterflies, birds have tiny microscopic structures on their feathers that the light goes thru a series of reflections in which only the blue color wavelength is escaped and the other wavelengths are canceled out. Think of the scenarios of how a prism would split the natural light into different wavelengths to separate the colors and the process of a noise cancellation headphone.

If you look at a Blue colored bird carefully in different angles you would notice that the depth of the blue color changes based on the angle you are looking at.

So does blue pigmentation ever occur naturally?

Obrina Olivewing Butterfly © Notafly – self-made Own photograph. Nikon. Studio., CC BY-SA 3.0

Yes! as far as my knowledge goes, THE ONLY animal with true blue pigmentation is the Obrina Olivewing Butterfly (Nessaea obrinus).

If blue is so hard to be made naturally, Then why blue is so popular?

I suppose the answer to this is in the question itself.

“Waterlilies and Japanese Bridge” by Claude Monet, 1899. Photo Credit: Princeton University Art Museum/Art Resource, NY.

Until recent synthetic color-making technologies, Blue color was the rarest. Therefore anything associated with the color blue was considered privileged.  Think of the Royal Blue and old aged most expensive paintings done with the color blue (ex. Picasso’s Blue period).


So to answer our previous poll question on Instagram, Were those feathers of birds truly Blue (pigmented), the answer is NO. It’s only an optical illusion.

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