Click to change the layer above the ball, it never changes, but your brain will make it seem like it does.
What: The official name for this optical illusion, is Color Assimilation[1] or the Bezold Effect[2], which would be the most concise way of describing what is happening here. If the illusion is working correctly, as it does on me, you will see a grey ball, with a multi-striped background with one layer of overlaying lines, to your eyes, the grey ball will assume the color of its overlaying stripes. As you change which color lines specifically overlay, the ball will follow suit again, even though it remains grey the entire time.
How To: Unless you’re color blind, you should be able to see this effect relatively quickly, and it should be quite strong. Click or tap on the screen and you’ll see the ball moving to where your cursor is, the ball is unequivocally and always grey, but your brain will meld it with the colors of the lines above it.
You can change the colors of the lines, the thickness, and the spacing to see how far you can push the effect. The smaller lines have a more powerful impact for me, which makes sense considering that means there is more color overlaying the ball. Changing up the colors of the lines and ball is also interesting, again, to me the bigger the contrast in the colors the more the effect appears.
As a small bonus, the grey gradient on the ball also gives some optical effect (email me if you know the name), that makes the lines not seem completely parallel to each other.
Explain it: Color assimilation, also known as the Bezold effect, is a well-documented phenomenon that occurs due to the way our eyes and brain process colors. Essentially, our brain merges adjacent colors subconsciously, creating a blending effect. This effect is particularly pronounced when colors are arranged in patterns, such as stripes, and becomes even stronger in patterns like checkerboards, where the interaction between colors is more intense.
Scientifically, this effect is linked to the way our visual system integrates information from neighboring regions in the visual field. The cones in our retina, responsible for color vision, send signals to the brain that are processed in a context-sensitive manner. This means that the perception of a color can be influenced by the colors surrounding it. Neural mechanisms in the visual cortex further integrate these signals, leading to the assimilation effect where colors appear to blend.
I've researched these optical illusions in my spare time but am clearly not any kind of expert and my explainations are pretty smooth brained, if you find something mis-cited, earlier examples, or general mistakes please new let me know via [email protected], be kind!