When you look at blue sky overhead or gaze across the seemingly endless expanse of a blue ocean, you would possibly think that the colour blue is common in nature.
But among all the hues found in rocks, plants & flowers, or within the fur, feathers, scales & skin of animals, blue is surprisingly scarce.
We are able to see color because each of our eyes contains between 6 million & 7 million light-sensitive cells called cones. There are three differing types of cones within the eye of an individual with normal color-vision , and every cone type is most sensitive to a specific wavelength of light: red, green or blue. Information from many millions-of-cones reaches our brains as electrical signals that communicate all the kinds of light reflected by what we see, which is then interpreted as different shades-of-color.
When we look-at colourful object, like a sparkling sapphire or a vibrant hydrangea bloom, “the object is absorbing a number of the white light that falls onto it; because it’s absorbing a some of light , rest of light that’s reflected has color,” science writer Kai Kupferschmidt, author of “Blue: In Search of Nature’s Rarest Color” (The Experiment, 2021).
“When you see a blue flower — as an example , a cornflower — you see the cornflower as blue because it absorbs the red a part of the spectrum,” Kupferschmidt said. Or to place it differently , the flower appears blue because that color is that the a part of the spectrum that the blossom rejected, Kupferschmidt wrote in his book, which explores the science & nature of this popular hue.
In visible-spectrum , red has long wavelengths, meaning it’s very low-energy compared with other colors. For a flower to seem blue, “it must be able to produce a molecule which can absorb very small amounts of energy,” in-order to absorb red a part of the spectrum, Kupferschmidt said.
Generating such molecules — which are large & sophisticated — is difficult for plants to-do, which is why blue flowers are produced by fewer than 10% of the world’s nearly 300,000 flower-plant species. One possible driver for evolution of blue flowers is that blue is highly-visible to pollinators like bees, and producing blue blossoms may benefit plants in ecosystems where competition for pollinators is high, Adrian Dyer, an professor & vision scientist at the Royal Melbourne Institute of Technology in Melbourne, Australia, told the Australian Broadcasting Company in 2016.
As for minerals, their crystal structures interact with ions (charged atoms or molecules) to find out which parts of the spectrum are absorbed and which are reflected. The mineral lapis lazuli , which is mined primarily in Afghanistan & produces the rare blue pigment ultramarine, contains trisulfide ions — three sulfur atoms bound together inside a crystal lattice — which can release or bind one electron.
“That energy difference is what makes the blue,” Kupferschmidt said.
Blue animals’ colors don’t come from chemical pigments. Rather, they rely-on physics to make a blue appearance. Blue-winged butterflies within the Morpho genus have intricate, layered nanostructures on their wing scales that manipulate layers of light in order that some colors cancel one another out and only blue is reflected; similar effect happens in structures found within the feathers of blue jays (Cyanocitta cristata), the scales of blue tangs (Paracanthurus hepatus) and therefore the flashing rings of venomous blue-ringed octopuses (Hapalochlaena maculosa).
Blue shades in mammals are even rarer than in birds, fish, reptiles & insects. Some whales & dolphins have bluish skin; primates like golden snub-nosed monkeys (Rhinopithecus roxellana) have blue-skinned faces; & mandrills (Mandrillus sphinx) have blue faces and blue rear ends. But fur — a trait shared by most terrestrial mammals — isn’t naturally bright-blue (at least, not in visible-light . Researchers recently found that platypus fur glows in vivid-shades blue & green when exposed to ultraviolet (UV) rays.
“But it takes lot of-work to-make this blue, then another question becomes: What are the evolutionary reasons to create blue? what is incentive?” Kupferschmidt said. “The fascinating thing once you dive into these animal worlds is usually , who’s the recipient of this message and may they see the blue?”
For example, while humans have 3 light-sensing receptor types in our eyes, birds have a 4th receptor type for sensing UV light. Feathers that appear blue to human eyes “actually reflect even more UV light than blue light,” Kupferschmidt explained. By that reasoning, the birds that we call blue tits (Cyanistes caeruleus) “would probably call themselves ‘UV tits,’ because that is what they might mostly see,” he said.
Because of blue’s scarcity in nature, the word for blue was a relative latecomer to languages round the world, appearing after the words for black, white, red & yellow, consistent with Kupferschmidt.
“One theory for this is often that you simply really only need to name a color once you can dye-things — once you can divorce colour from its object. Otherwise, you do not actually need the name for the colour ,” he explained. “Dyeing things blue or finding a blue pigment happened really late in most cultures, and you can see that within the linguistics.”
The earliest use of blue dye dates to about 6,000 years ago in Peru, and therefore the ancient Egyptians combined silica, calcium-oxide & oxide to make a long-lasting blue pigment referred to as irtyu for decorating statues, researchers reported Jan. 15 within the journal Frontiers in Plant Science. Ultramarine, a vivid blue pigment ground from lapis lazuli , was as precious as gold in medieval Europe, and was reserved primarily for illustrating illuminated manuscripts.
Blue’s rarity meant that people-viewed it as a high-status color for thousands of years. Blue has long been related to the Hindu deity Krishna & with the Christian Virgin Mary, and artists who were famously inspired by blue in nature include Michelangelo, Gauguin, Picasso and van Gogh , consistent with the Frontiers in Plant Science study.
“The relative scarcity of blue available in natural pigments likely fueled our fascination,” the scientists wrote.
Blue also colors our expressions, appearing in dozens of English idioms: you might work a blue-collar job, swear a blue streak, sink into a funk or talk until you’re blue in face, to name just a couple of . And blue can sometimes mean contradictory things-depend on idiom: “‘Blue sky ahead’ means a bright future, but ‘feeling blue’ is being sad,” Kupferschmidt said.
Blue’s scarcity in nature may have helped shape our perception of colour & things that appear blue. “With blue, it’s sort of a whole canvas that you simply can still paint on,” Kupferschmidt said. “Maybe because it’s rare in nature and perhaps because we associate it with things that we cannot really touch, just like the sky and therefore the sea, it’s something that’s very-open different associations.”