What you see is a sprite with short gray stripes, and a backdrop with stripes filling the stage. ☛ Click to change the color of the backdrop stripes. Note how the short stripes appear to change color. ☛ Click the blue button to set the short stripes to a random color and brightness. ☛ Click the green flag to switch back to gray short stripes.
If you aren't convinced that the short stripes are indeed the same color and brightness regardless of backdrop, look inside. Based on an illusion in the book Optical Illusions by Gianni A. Sarcone.
