tl;dr: UC Berkeley researchers used adaptive optics laser ophthalmoscopy to selectively stimulate only M cone cells in the retina, producing "olo"—a highly saturated blue-green color outside the normal human visible gamut, seen so far by only five people. The closest sRGB approximation is #00FFCC, though some scientists dispute whether it qualifies as a genuinely new color. The team is exploring applications for treating color blindness and potentially enabling tetrachromatic vision.