The famous checkerboard illusion... I was going to do a version of this but since someone already beat me to it... https://commons.wikimedia.org/wiki/File:Grey_square_optical_illusion.svg . The squares under A and B are the same color. You can test this using any graphics program that has an "eye dropper" (color picker) tool.
Checker Shadow Illusion free icon was designed by GDJ for icons Png and presented to its users.
GDJ
2/17/2018