I like optical illusions, and this is no exception (click to enlarge):
You see embedded spirals of green, pinkish-orange, and blue right?
Incredibly, the green and the blue spirals are the same colour! The reason they look different colours is because our brain judges the colour of an object by comparing it to surrounding colors. In this case, the stripes are not continuous as they appear at first glance.
The orange stripes go through the “green” spiral but not the “blue” one. So without us even knowing it, our brains compare that spiral to the orange stripes, forcing it to think the spiral is green. The magenta stripes make the other part of the spiral look blue, even though they are exactly the same colour. Read more here and see more here. The stripes are actually both this colour: