How to see “impossible colors”
What does “reddish green” look like? Not brown, not olive — an actual color that’s simultaneously red and green the way cyan is simultaneously blue and green. You can’t picture it. Neither can I. These are called “impossible colors and the reason is neurological. Our eyes have opponent color channels: one processes red versus green, another handles blue versus yellow. These channels work by opposition — when one fires, it suppresses the other. Red and green can’t both be “on” at the same intensity any more than a light switch can be up and down simultaneously. The same goes for blue and yellow.
Some researchers claim they’ve made people see impossible colors through special visual experiments. In one technique, subjects stare at adjacent red and green stripes until the boundary dissolves. Some report perceiving a color they’ve never seen before — neither red nor green but somehow both. Others have used eye-tracking to stabilize images on the retina, preventing the normal flicker that allows opponent channels to take turns. The results are disputed. Some subjects report transcendent experiences; others just see mud.
Whether impossible colors can truly be perceived or are just an artifact of exhausted neurons remains debated. But the attempt reveals something profound: color isn’t “out there” in the world. It’s a construction of our brains, with hard limits built into the architecture.