Ok Smart Guy. Find The Curved Line.

[LevelUP]

To be fair, in real life they would be very different shades. This is not so much an optical illusion as it is a reminder that digital representations do not necessarily correlate to the physical world. It's still kind of cool though.

What is happening is that your brain is tricking you to believe that one of the square boxes is in the shade when it isn't. They are both pixel perfect the same exact color of rgb(155, 155, 155). This works if you print out the image as well.