Follow the circled dot with your eyes as the ring turns: it keeps changing color all the time.
Tricks of motion
Motion silencing
Look at the middle. The dots keep changing color. What happens when the ring starts to turn?
They seem to stop changing, though they change just as fast.
Why? Your brain has trouble seeing a change in something that is also moving.
Picture: Drawn by Science Playground · Wikipedia(opens in a new tab)