In a groundbreaking study published in Science Advances in April 2025, researchers at the University of California, Berkeley, have unveiled a previously unseen color, termed "olo." This discovery was achieved through a novel technique that directly stimulates specific photoreceptor cells in the human retina, leading to the perception of a highly saturated blue-green hue unlike any naturally occurring color.

Human color vision relies on three types of cone cells in the retina: S-cones (short-wavelength, sensitive to blue light), M-cones (medium-wavelength, sensitive to green light), and L-cones (long-wavelength, sensitive to red light). Typically, these cones work in combination to allow the perception of a wide spectrum of colors. However, isolating the stimulation of a single type of cone to perceive a unique color has not been achieved until now.

The Berkeley research team developed a method called "Oz"—named after the green-tinted glasses in "The Wizard of Oz"—to selectively stimulate individual M-cones without activating S- or L-cones. This was accomplished using precise laser microdoses targeted at the M-cones. The process required detailed mapping of each participant's unique cone layout, achieved through advanced imaging techniques such as adaptive optics optical coherence tomography (AO-OCT). This mapping allowed the researchers to identify and stimulate specific M-cones accurately.

Five participants underwent the Oz procedure, including some of the researchers themselves. They reported perceiving a highly saturated blue-green color, unlike any naturally occurring hue, which they named "olo." One participant described it as "a beautiful, ultra-intense teal." The name "olo" is derived from the binary code "0, 1, 0," representing the selective stimulation of M-cones (1) while S- and L-cones remain unstimulated (0).

This discovery offers new insights into human color perception and the brain's interpretation of visual stimuli. The ability to selectively stimulate specific photoreceptors could have significant applications, including:

• Studying Vision Mechanics: Providing a novel method to investigate how the brain processes color information.
• Simulating Eye Diseases: Allowing researchers to replicate the effects of various visual impairments for better understanding and treatment development.
• Treating Color Blindness: Potentially restoring color perception in individuals with color vision deficiencies by compensating for missing or defective photoreceptors.

However, the current technology has limitations, such as requiring peripheral vision and precise eye tracking, making it unlikely for immediate consumer applications like enhanced digital displays.

While the discovery has been met with enthusiasm, some experts remain skeptical. John Barbur of King's College London suggests that "olo" may not be a new color but rather an intensified version of green. He argues that the value of the discovery is limited, as it might not represent a fundamentally new visual experience.

The revelation of "olo" has sparked interest beyond the scientific community. Artists and designers are intrigued by the possibility of expanding the color palette, and discussions have emerged about the subjective nature of color perception. The discovery challenges our understanding of the visual world and opens up new avenues for exploring human sensory experiences.

In summary, the identification of "olo" represents a significant advancement in the field of vision science, offering both new challenges and opportunities for future research and applications.