The cause depends on chemistry, physics, and how we see colors. Among all the types of rocks, in plants and flowers, or in the fur, feathers, scales, and skin of animals, blue is surprisingly scarce.
If you think of the sky or the ocean, you might think that the color blue is common in nature, but the reality is quite different. Among all the types of rocks, in plants, flowers, fur or feathers or animal scales, this hue is surprisingly scarce. The reason depends on the chemistry and physics through which colors are produced, but also on how we see them. Explaining scientifically why the blue hue is so rare in the environment is writer and journalist Kai Kupferschmidt, author of the book "Blue: In Search of Nature's Rarest Color." The text explores the science and nature of this hue and how it is visually received by the human eye.
Why the color blue is rare in nature
Each of our eyes contains between 6 million and 7 million light-sensitive cells called cones that allow us to see different shades of colors. There are three different types of cones in the eye of a person with normal vision and no eye disease. Each type of cone is more sensitive to a particular wavelength of light: red, green or blue. Information from millions of cones reaches our brains as electrical signals that tell us all the types of reflected light we see, translating them into different shades of color.
When we look at a colored object, for example a sapphire or a hydrangea flower, "the object absorbs some of the white light falling on it" while the rest of the reflected light has color, science writer Kai Kupferschmidt explained to WordsSideKick.com. "When you see a blue flower, like a cornflower, you see it blue because it absorbs the red part of the spectrum," the author said. Basically, the flower appears blue because that color is the part of the spectrum that the plant has rejected. For a flower to appear blue, "it must be able to produce a molecule that can absorb very small amounts of energy," to absorb the red part of the spectrum.
The generation of such molecules, which are large and complex, is difficult for plants to accomplish, which is why blue flowers are produced by less than 10 percent of the nearly 300,000 plant species worldwide. As for minerals, their crystal structures interact with ions to determine which parts of the spectrum are absorbed and which are reflected. The mineral lapis lazuli, which produces the rare ultramarine blue pigment, contains trisulfide ions - three sulfur atoms bound together within a crystal lattice - that can release or bind a single electron. It would be this difference in energy that would give it the blue hue.
Among animals, blue is even rarer. For example, the blue-winged butterflies of the genus Morpho have intricately layered nanostructures on their wing scales that manipulate layers of light so that some colors cancel each other out and only blue is reflected. But animal fur is never naturally this color in visible light. The rarity of blue has caused people to consider it a high-ranking color for thousands of years, but scientists are also studying why shades of this color are prevalent and well evidenced in some species.
Resting in the world of terrestrial fauna, it is being observed that some animal species are shrinking and the phenomenon would not have a positive cause.