(title pic via reddit)
No they arent, the lower box is obviously part grey and part white. I mean, if you cover the stripes on a zebra with masking tape that doesnt make it black. Or white depending on which stripes you color.
Look up Josef Albers’ work on how our perception of a color is changed by the color that surrounds it. It’s one of the foundational concepts in modern painting.
No he is correct. The top of the lower box is white. The illusion that they are the same color is created when you use your finger to cover the part of the lower box that is a different color. His zebra/masking tape analogy is spot-on.