I noticed it as a child.
If I close my right eye, the world just looks ... colder. White walls take on a very subtle blue or green tint. If I close my left eye, the world becomes a bit warmer, as if filtered by very pale rose glass.
The effect is extremely, extremely subtle. It's not like my eyes are covered with red-blue 3D glasses. It's as if someone pulled up a color slider in Photoshop and adjusted the hue in each eye by just one tiny notch. I'd lie in bed as a 5-year-old and play this game — closing one eye and then another — and find wonder in the weirdness of it.
So I asked a handful of visual perception experts to find out: Is this real?
It's actually quite plausible that each eye sees color slightly differently
Overall, the experts replied, I'm not crazy (at least about this). It's very common to find a subtle but significant difference between the eyes on color perception tests.
Steven Shevell, a professor of ophthalmology and psychology at the University of Chicago, frequently tests color vision by bringing people into the lab and gradually changing hues of light until the participant notices a difference. "Both eyes will be slightly different but in the normal range [meaning not colorblind]," Shevell tells me. (These tests also find slight differences between people in color perception, though the differences are small here too.)
The reason boils down to this: We're not perfectly symmetrical creatures. Just as the fingers on my right hand may be slightly shorter than the ones on my left, my left and right eyes may have slight differences.
Color perception is an amazingly complicated process. It's not just about the physical properties of light entering your eye through a lens. It's about the biology of the receptors in the back of your eye, and then the neural pathways that make sense of them. Small differences in any one of those areas can cause tiny differences in color perception.
"These differences are small compared to the range of colors that we see, but large enough to be above measurement error," David Brainard, a psychologist at the University of Pennsylvania who studies human vision, writes me in an email.
Brainard says the research points to the differences in cone cells — which detect color — as the main reason two eyes in the same body will each see slightly different colors. It's "not their chemical composition, but rather the density with which they are packed into individual cones, which in turn affects very slightly the way they respond to light of different wavelengths," he says.
The lens may play a small role, as well.
"In general, the crystalline lens in our eyes becomes increasingly yellow as we age (primarily due to sunlight exposure), allowing less and less blue light to reach the retina," Jonathan Winawer, a professor of psychology and neuroscience at New York University, writes me in an email. One eye could conceivably be yellowing faster than the other. (This probably isn't a factor in my case, since I remember seeing slightly different colors as child.)
For the most part, the brain can compensate for the physiological differences between the eyes, Don MacLeod, a UC San Diego psychologist who studies human vision, explains. "But maybe the compensation is not quite perfect," he writes in an email.
The experts I consulted also added this: There are some medical conditions that can bring on sudden changes in color perception in one eye and not the other. If you feel like something's up with your vision, as always, consult a doctor, not the internet. (It's also possible to be colorblind in only one eye, but that is an extremely rare condition.)