Tired eyes
McCollough effect
Press Try it: red stripes lying down and green stripes standing up take turns for 3 minutes. Let your eyes wander over them. Then what color are these black and white stripes?
The stripes lying down look a little green, and the ones standing up a little pink. Tilt your head sideways and the colors swap places.
Why? Your brain links a color to the direction of the lines and keeps the link for a surprisingly long time. Scientists are still not sure why.
Picture: Android Mouse, Urutseg, Public domain · Wikipedia(opens in a new tab)