I believe you are talking about the color blindness tests where the numbers are written in colored dots. Basically if you are not color blind you will see the numbers but if you are color blind then you will only see a bunch of dots.
Optical illusions were first used by the Greeks when they built their temples. They built there roof on a slant which made an illusion to make it look like the roof was actually straight.
Strictly speaking, no, but they do provide the illusion of animation which is not real, as flip books are just books with a series of images that vary slightly from one to the next, so that when the...