Tricks of color
Chromostereopsis
Do the red and the blue lie at the same depth?
They are on the same flat screen, but for most people the red floats in front of the blue.
Why? Your eye’s lens bends blue light more than red, so the two colors land in slightly different places at the back of each eye. Your brain reads the difference as depth.
Picture: Fred the Oyster, CC0 · Wikipedia(opens in a new tab)