As we’ve learned time and again with optical illusions like the infamous white and gold dress (or was it black and blue?) and the confetti circles, the human brain isn’t always an objective judge when it comes to color.
As SYFY WIRE explains, we use context clues—lighting, the color of nearby objects, etc.—to discern the color of a given item. If you move that item in and out of different surroundings, your brain may perceive the item itself to be changing color.
Case in point: the optical illusion below, developed by Akiyoshi Kitaoka, a psychology professor at Ritsumeikan University in Osaka, Japan. In the video, you see an orange square sitting atop a sheet of paper whose gradient transitions from red on the left to yellow on the right. When the square is in the middle, it’s basically invisible against the matching orange backdrop. But as it slides into the yellow region, it appears to grow darker—even red. As it’s moved back across the paper and into the red region, it seems like a lighter orange than before.
Kitaoka has an entire website dedicated to showcasing his optical illusions, some of which explore perceived color changes similar to the one above. Overall, these types of illusions help illustrate how much information our eyes use to make decisions about what color something is. Take, for example, the classic checker shadow illusion, which shows a checkered grid partially under what appears to be the shadow of a tall cylinder. Box A, which isn’t in shadow, looks darker than Box B, which is. Our brains assume that since A and B are the same color under different circumstances, B must actually be lighter than A—so that’s how we perceive it. If you isolate Boxes A and B, however, you’ll find that they’re really the same exact color. You can watch that process in the video below.
[h/t SYFY WIRE]