Color surprises from the high-tech present and the ancient past

 

New hue! Who knew?

It’s not every day that you get to see something no one in the world has seen before. But Ren Ng and four of his colleagues are lucky enough to have had that experience.

A few months ago, Ng sat down next to a laboratory table covered with a maze of lasers, lenses, mirrors, and other optical engineering gizmos. Then he let his fellow researchers focus a laser beam—eye-safe, worry not—into his dilated pupil.

The University of California, Berkeley, electrical engineering and computer science professor was the second subject of an experimental system he and his colleagues designed to make the eye perceive an unnatural color. When weak laser pulses hit thousands of light-perceiving cone cells in his retina, a small green square the same color as the laser light slowly appeared in his vision. Gradually, as the team focused the laser more precisely, the color became more and more blue-green. “And at some point, as it really gets perfected, you're like ‘Wow,’” Ng tells Newscripts.

The hypersaturated blue-green he experienced seeing is imperceptible to humans under natural circumstances. The researchers are calling the color “olo” (Sci. Adv. 2025, DOI: 10.1126/sciadv.adu1).

Declaring olo the Pantone color of the year could be tough, given that people can’t see it without laser stimulation. That’s because of the way human eyes work. The eye has three types of cone cells. Each is sensitive to a spectrum of short (S), medium (M), or long (L) wavelengths. Those spectra overlap, and the middle M spectrum is completely overlapped by the S and L ones.

“There’s no wavelength that only triggers M cells,” Ng says. So anytime you see a green that falls in the M spectrum, it’s muddled with shorter wavelength blue or longer wavelength red.

The researchers’ new technique, dubbed Oz—inspired by the green-tinted glasses that Emerald City residents wear in the original Wizard of Oz books—simulates only the M wavelengths. They do that by scanning cone cells one by one with an infrared light, measuring how each cell changes shape—which depends on the type of cell it is—and then delivering green light only to the M cells.

This is all very complicated, of course, which is why Ng didn’t immediately see olo. “It's not like we flip a switch to turn it on.”

Beyond revealing novel colors, the team hopes the method could be harnessed to understand more about color blindness or diseases that affect vision.

Earth’s emerald oceans

Here’s one color surprise humans never got to see. From 3 billion years ago to roughly 600 million years ago, the Earth’s oceans were green, not the blue that we're used to.

Physicist Taro Matsuo at Nagoya University and colleagues concluded this while trying to understand why cyanobacteria, commonly called blue-green algae, evolved to have a pigment called phycoerythrobilin in addition to chlorophyll for photosynthesis. Chlorophyll reflects green light—giving leaves their color—but phycoerythrobilin absorbs green light.

Cyanobacteria are thought to have induced the so-called Great Oxidation Event that led to complex life on Earth. But let’s rewind to the Archaean eon, which started roughly 4 billion years ago, before photosynthesis was a thing. In those earliest days, the oceans were full of dissolved ferrous iron. Then, as photosynthetic organisms evolved and released oxygen into water, ocean chemistry changed. The gradual oxidation of ferrous iron created iron hydroxide precipitates.

Matsuo and colleagues ran computer simulations to figure out the distributions of oxygen, reduced iron, and iron hydroxide in the ancient oceans. Because iron hydroxide absorbs blue light and water absorbs warm reddish colors, the simulations showed that surface waters would have appeared green. The team was initially skeptical about the idea of green Archaean oceans, Matsuo says, but it explains how cyanobacteria evolved both types of photosynthetic pigments (Nat. Ecol. Evol. 2025, DOI: 10.1038/s41559-025-02637-3).

Two things corroborate the hypothesis: the researchers found that genetically engineered cyanobacteria containing phycoerythrobilin grow better in green waters, and cyanobacteria thrive in the greenish waters around the Japanese volcanic island of Iwo.

The work highlights the interplay between chemistry and evolution, Matsuo tells Newscripts via email. “While Earth serves as a cradle for life, life also shapes the Earth itself, contributing to what makes our planet unique.”

Please send comments and suggestions to newscripts@acs.org.