Which square is lighter, A or B?
(Attachment Link)
It depends on whether you're talking about the pixels, or the fact it clearly represents a 3D image, with the green cylinder casting a shadow over B?
These option illusions the brain's advanced visual processing, rather than uselessness. The brain has processes visual information, rather than just interpreting it literally in order for our survival. For example, it's often better to ear on the side of caution and assume a dark spot on the ground is a hole, rather than just a painted area.