In ~Science and not ~food_and_drink because it's actually about optical illusions, really:
The principle is based on the confetti illusion, a visual phenomenon where the perception of colors is strongly influenced by its surrounding context. In this optical illusion, a neutrally colored ball is placed within a grid of differently colored lines. When the lines of a particular color are in the foreground, the ball's color appears to blend with that of the lines.
Also applies to lemons in yellow bags and some other stuff.