Optical Wonderful
Color & Contrast Illusions
Illusions built from how the brain interprets color and brightness relative to their surroundings, rather than in isolation - proof that what you 'see' is a judgment call, not a measurement.
"The Dress" (Blue/Black vs White/Gold)
The 2015 photo that split the internet into blue-and-black and white-and-gold. Why it happens, and a poll testing whether night owls really see it differently.
Color & ContrastChecker Shadow Illusion
Two squares on a checkerboard, one in shadow, are exactly the same grey, but almost nobody sees it until a bridge joins them. Why the brain reports surfaces, not light.
Color & ContrastHermann Grid Illusion
A plain grid of black squares makes grey smudges flicker at the crossings you aren't looking at. The textbook explanation, and why it's probably wrong.
Color & ContrastSimultaneous Contrast Illusion
Two identical greys look different on dark and light backgrounds. Why the brain judges brightness and colour by comparison, from Chevreul's dye works to today.