Yeah I remember this picture from high school haha. It used to freak me out too but if you stare at B with A in your peripheral you can see they're 're the same colour.
@bookerdana The Shadow darkens the light color to the same as the unshadowed dark. But because it also shadows the dark color to be darker as well, our brain is able to recognize the pattern and 'corrects' our perception to show said continued pattern.
