Our eyes don't work like cameras, passively recording whatever is in front of them. Instead, our brain actively interprets visual information, and a huge part of that interpretation is context. The things surrounding an object can dramatically change how we perceive that object's color, brightness, or even shape. This effect is called assimilation.

Imagine a light gray stripe. If you place it on a background of very light yellow stripes, the gray stripe itself might start to look a bit yellowish. Its color appears to assimilate, or be pulled toward, the color of its background. The lines between the object and its context start to blur, and our brain averages them out.

Assimilation is often confused with its opposite: contrast. While assimilation makes an object look more like its surroundings, contrast makes it look less like its surroundings. Our visual system uses both tricks to make sense of the world.

Think about a medium gray square. If you put that square on a black background, it looks lighter. If you put the exact same square on a white background, it looks darker. That's a contrast effect. The background exaggerates the difference between itself and the object.

The key difference often lies in the pattern of the background. Assimilation tends to happen with fine, repeating patterns like thin stripes, while contrast effects are more common with large, solid backgrounds.

This effect isn't just a neat party trick; it's fundamental to how we see. One of the classic examples is the Munker-White illusion. In this illusion, identical objects appear to be different shades because of the colors striped over them.

Look at the graphic below. The horizontal gray bar is a single, uniform color from left to right. However, the section on the white stripes probably looks darker than the section on the black stripes. The gray is assimilating the properties of the stripes behind it.

Your brain sees the gray bar next to the white stripes and thinks, "This area is mostly bright," so it darkens the gray in comparison. When it sees the gray next to the black stripes, it thinks, "This area is mostly dark," and lightens the gray. The context is rewriting reality.

Understanding assimilation helps explain why choosing a paint color at the hardware store can be so tricky. A color swatch that looks perfect under the store's fluorescent lights and next to other swatches can look completely different on a large wall in your home, surrounded by your furniture and illuminated by natural light. The color of the swatch assimilates with its new, much larger context.

By seeing how context can bend our perception of reality, we get a better sense of the active, interpretive work our brain does every moment we have our eyes open.