Here's a cool illusion I found via UCLA neuroscientist Matt Lieberman on Twitter. There are no red pixels in this image:
You can confirm it using software like the Digital Color Meter that comes installed on Macs. Or for a low-tech demonstration, form a tube with your hand, then look through it with one eye so you can only see a small patch of the screen. In isolation, the pixels are grey or blue—definitely not red. But when your brain combines the knowledge that strawberries are red with an automatic correction for lighting conditions, they sure look red. In the real world, that's a good thing; you wouldn't want strawberries that appear to change colour when you enter a room with different lighting.
It's another reminder (like that colour-changing dress before it) that your brain is doing a lot of computations behind the scenes, without your knowledge or effort. Take care of your brain, because even if you don't know it, it's taking care of you.