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What: The official term for this optical illusion is Color Assimilation or the Bezold Effect, which is the most succinct way to explain what's going on here. If the illusion functions properly, as it does for me, you'll notice a grey ball set against a multi - striped background with a layer of overlying lines. To your eyes, the grey ball will take on the color of the overlying stripes. As you change the specific color of the overlying lines, the ball will change its apparent color again, even though it stays grey throughout.

How To: Unless you're color - blind, you should be able to observe this effect fairly rapidly, and it should be quite noticeable. Click or tap on the screen, and you'll see the ball move to the position of your cursor. The ball is definitely and always grey, but your brain will combine it with the colors of the lines above it. You can modify the colors of the lines, their thickness, and the spacing to see how much you can enhance the effect. For me, thinner lines have a stronger impact, which is reasonable since it means there's more color covering the ball. Changing the colors of the lines and the ball is also fascinating. Again, to me, the greater the color contrast, the more pronounced the effect seems. As a little bonus, the grey gradient on the ball also creates some optical effect (email me if you know its name), making the lines seem not entirely parallel to each other.

Explain it: Color assimilation, also referred to as the Bezold effect, is a well - documented phenomenon that happens because of how our eyes and brain process colors. Essentially, our brain subconsciously combines adjacent colors, producing a blending effect. This effect is especially prominent when colors are arranged in patterns like stripes and becomes even more intense in patterns such as checkerboards, where the interaction between colors is stronger. Scientifically, this effect is related to how our visual system integrates information from neighboring areas in the visual field. The cones in our retina, which are responsible for color vision, send signals to the brain that are processed in a context - sensitive way. This means that the perception of a color can be affected by the surrounding colors. Neural mechanisms in the visual cortex further integrate these signals, resulting in the assimilation effect where colors seem to blend.