Scottish musician Caitlin McNeill posted an image of a dress on Tumblr with the question, “guys please help me – is this dress white and gold, or blue and black?  Given the virtual explosion of interest that resulted (answer is blue and black, BTW), I thought I would share this famous illustration designed to demonstrate how easily the the human visual system can be fooled. Which is darker? Square A or square B. The answer is that they are both the same color and brightness. Cut two holes in a piece of paper so you can compare the two squares while obscuring the background if you do not believe me.