Optical illusions ... arm is a darker or lighter shade, creating the illusion of contrast. But the truth is, the whole "X" uses only one single shade of red. The same goes for the green ...

A head-scratching optical illusion challenges the perception of ... Despite the lettering remaining the same color, where the characters appearing darker or lighter depending on where they fall ...

The science behind #shoegate explains why some people see grey ... optical illusions dupe our brain into seeing motion, others like the Mach bands illusion deceive us into seeing imaginary shades.

Nestled among the rugged terrain and blending flawlessly with its surroundings, a game bird has turned itself into a living optical illusion ... The grouse in the same color with tiny spots ...