This essay is adapted from Traversal.

We look at a thing — a bird, a ball, a planet — and perceive it to be a certain color. But what we are really seeing is the color that does not inhere in it—the portion of the spectrum it shirks, the wavelength of light it reflects back unabsorbed. Our world appears a swirling miracle of blue, but its blueness is only a perceptual phenomenon arising from how our particular atmosphere, with its particular chemistry and its insentient stubbornness toward a particular portion of the spectrum, absorbs and reflects light.

In the living world beneath this atmosphere that scatters the shorter wavelengths as they pass, blue is the rarest color: There is no naturally occurring true blue pigment among living creatures. In consequence, only a slender portion of plants bloom in blue, and an even more negligible number of animals are bedecked with it, all having to perform various tricks with chemistry and the physics of light, some having evolved astonishing triumphs of structural geometry and optics to render themselves blue. Each feather of the blue jay is tessellated with tiny light-reflecting beads arranged to cancel out every wavelength of light except the blue.

The Morpho peleides butterfly, singular and striking with its enormous cobalt blue wings, is covered with miniature scales ridged at the precise angle to bend light in such a way that only the blue portion of the spectrum is reflected to the eye of the beholder — a variation on diffraction grating, the technique astronomers use inside telescopes to fan light into a rainbow in order to study each color of light individually, decoding the chemical composition of the star observed by the absorption pattern at the various wavelengths, uniquely absorbed by different atoms. Of all the known animals, only a handful of butterfly species produce pigments as close to blue as nature can get — a green-tinted aquamarine the color of Uranus.

In 1990, the Voyager spacecraft completed its epoch-making mission of surveying the outer Solar System with a triumphal final photograph of Neptune, rendered a stark cobalt blue by a methane atmosphere that so readily inhales the red and infrared wavelengths. Then, before its cameras blinked shut for eternity, before continuing on its vectorless voyage to travel farther from Earth than any human-made vessel, Voyager turned its enormous mechanical eye toward its origin planet — a pixel of barely distinguishable blue across the expanse of 30 astronomical units, an unfathomable four and a half billion kilometers away. With the camera’s optics unequal to this sweep of spacetime, the photograph had no apparent scientific value. It was a poetic gesture, the permission for which the poetic astronomer Carl Sagan had spent years petitioning unpoetic NASA administrators.

In the grainy image that came back, Earth appeared the way Whitman had seen it in his mind’s eye, the poet’s eye, a century ahead of the spacecraft engineer’s — “a blue point, far, far in heaven floating.” Sagan saw it as a precious “pale blue dot” beckoning us to cherish and preserve it, this “only home we’ve ever known.” A home whose blue mystery we know no better than we know our own depths.

An epoch earlier, the aspiring poet turned pioneering chemist Humphry Davy, whose 1799 experiments with nitrous oxide became the first systematic study of altered consciousness, traveled to Italy, where he collected samples of crystals for a series of chemical experiments that would unravel the chromatic secrets of the ancient world. First in Rome, among the remnants of the baths of Titus, and again on a small pot in the ruins of Pompeii, he discovered an arresting deep blue he identified as Egyptian blue — humanity’s first synthetic pigment, manufactured by the ancients from the rare mineral lapis lazuli, which they mined in the Sar-e-Sang valley of present-day Afghanistan and turned into the stunning blue that occupied a special symbolic place in their art as the color of the sky and the life-river Nile, a chromatic echo of the universe itself. Their methodology for transforming crystal into pigment, matter into meaning, had been lost during the Dark Ages, leaving millennia of artists and natural philosophers to speculate on the secret of the richest blue. Upon his return from Italy, Davy published a paper humbly titled Some Experiments and Observations on the Colours Used in Painting by the Ancients. In it, he demonstrated that Egyptian blue — chemical formula CaCuSi₄O₁₀ — is “a frit made by means of soda, and coloured by oxide of copper.” The color of creation, broken down to chemical code.

Two centuries later, the Madras-born, American-based chemist Mas Subramanian would accidentally discover, while conducting electrical experiments, the first new inorganic blue pigment since Davy’s day, the first safe synthetic alternative to the crowning chromatic glory of ancient Egypt: the deep, intense YInMn Blue — so named for its constituents: yttrium, indium, manganese. Nontoxic, unlike cobalt and Prussian blue, it withstands fading even when confronted with oil or water, and reflects infrared light; to paint a roof in YInMn Blue would be to keep the habitat beneath it cooler, more energy-efficient, more impervious to the solar radiation that gives life and vanquishes life. All this splendor and unsuspected might derive from its singular crystal structure, encoded in which is the subtle, bewildering reminder that even in a portion of the universe as slender and human-trammeled as synthetic pigments, there are wonders yet to be discovered.