A father-and-son team—one a graduate student studying animal behavior, the other an astrophysicist at Harvard—were discussing cephalopods over dinner when they stumbled onto something nobody else had considered. If octopuses are colorblind, seeing the world in shades of gray, how do they match the colors around them so perfectly? The answer might lie in the same optical flaw that telescope designers spend millions trying to eliminate.

The Problem with Being a Master of Disguise

Octopuses transform their appearance in milliseconds. A mottled brown octopus crawling over coral can flush white, then dapple itself in reds and yellows to vanish against the reef. This would be impressive for any animal. For one that sees only in black and white, it borders on impossible.

The issue is straightforward: octopuses have just one type of photoreceptor in their eyes. Humans have three types of cones, allowing us to distinguish millions of colors. Most mammals have two. Birds have four. Octopuses have one, which means they're seeing the world like an old black-and-white television. Yet somehow, they're matching colors they supposedly can't detect.

More than two-thirds of an octopus's brain is dedicated to processing visual information—slightly more than humans devote to the task. They're not just looking around. They're analyzing their environment with intense focus, despite missing the hardware that should make color vision possible.

The Telescope Flaw Theory

Alexander Stubbs and his father Christopher noticed something odd about cephalopod eyes: their pupils are deliberately weird. Where most eyes evolve toward circular pupils that minimize optical distortions, octopuses have dumbbell-shaped pupils. Squid and cuttlefish have U-shaped or W-shaped openings. These shapes shouldn't work well. They should create blurry, distorted images.

That's exactly the point.

Chromatic aberration is what happens when a lens bends different wavelengths of light by different amounts—the same principle that makes prisms split white light into rainbows. Camera makers and telescope designers consider it a defect to be corrected. But the Stubbses proposed in 2016 that cephalopods might be using it as a feature, not fighting against it.

Light entering an octopus's oddly-shaped pupil comes in from multiple angles. Blue light focuses at a different depth than red light. By adjusting the shape of their eyeball—changing where the retina sits relative to the lens—an octopus could bring different colors into focus. The image would be blurry, but the type of blur would tell them what color they're looking at. Computer models showed that image contrast in these optical systems depends heavily on wavelength. An octopus would struggle to see a white object clearly but could precisely distinguish between yellow and blue.

The theory is elegant. It also might be completely wrong, or at best incomplete.

Skin That Sees

Three years before the Stubbses published their chromatic aberration hypothesis, researchers at UC Santa Barbara discovered something unsettling: octopus skin responds to light even when completely separated from the animal's body and brain.

Desmond Ramirez and Todd Oakley took skin samples from California two-spot octopuses and shone light on them. The chromatophores—tiny sacs of pigment embedded in the skin—expanded when exposed to light and contracted when the light switched off. The skin was reacting on its own, with no input from eyes or brain. Blue light triggered the fastest response.

The skin contains the same light-sensitive proteins, called opsins, found in octopus eyes. Specifically, they found rhodopsin in sensory neurons on the skin's surface. The process, which they named Light-Activated Chromatophore Expansion (LACE), responds most strongly to light at 480 nanometers—the same wavelength that octopus eyes are most sensitive to.

This doesn't mean octopus skin "sees" the way eyes do. The skin can't detect edges or shapes or movement. But it registers brightness and changes in light levels across the entire body surface. An octopus has millions of tiny light meters scattered across its skin, each one capable of triggering local color changes without waiting for instructions from the brain.

When the Ocean Does Half the Work

Both theories might be correct because the problem octopuses face isn't as hard as it first appears. Seawater acts as a color filter. Red and orange wavelengths get absorbed within the first few meters of depth. Below about 30 feet, everything trends toward blues and greens. The palette an octopus needs to match shrinks considerably.

Octopuses are also extra sensitive to contrast—they notice dark large shapes (predators) and light small shapes (prey) more readily than other visual patterns. They have a "rectilinear" bias, first documented in 1957, meaning they detect horizontal and vertical lines better than diagonal ones. And they can perceive polarized light, which allows them to see clearly through water without the distortion from reflections that hampers color-based vision.

The environment provides constraints. An octopus doesn't need to choose from millions of possible colors. It needs to match the limited palette available at its current depth, using a combination of eye-based cues (possibly chromatic aberration), skin-based light sensing, and texture matching through papillae—the bumps and spikes it can raise on its skin.

The Unanswered Question

Neither theory fully explains the speed and precision of octopus camouflage. Chromatic aberration would require constant adjustment of eye shape and careful analysis of blur patterns—possible, but slow. Skin-based sensing provides local information but no overall picture of what color pattern to create.

The most likely answer is that octopuses use both systems, plus others we haven't discovered yet. The skin provides a rough first pass, responding automatically to light levels. The eyes gather more detailed information, possibly extracting color through optical tricks. The brain, with its massive visual processing centers, integrates everything and coordinates the response across thousands of chromatophores.

What seemed like a simple question—how do colorblind animals match colors?—turns out to require rethinking what "seeing color" means. Maybe octopuses don't see color the way we do. Maybe they feel it with their skin, infer it from blur, and calculate it from the physics of light bending through water. The result is the same: an animal that disappears into its surroundings despite lacking the biological equipment we assumed was necessary for the job.