Question: Which square is darker?
(1) Square A (2) Square B (3) Neither
The correct answer is (3) Neither. Apparently your brain compensates for the shadow and so square B appears brighter. I answered (1) as square A looks so much darker, I assumed it a trick question (a number of previous questions’ correct answers were that they were the same). So I loaded it up into a graphics program and checked the RGB values of the squares. What amazed me was that not only were they the same, the effect of the brain recolouring square B is so strong, that the square itself looked a completely different colour to that shown by the dropper tool as shown below:
Which all leads to a rather obvious conclusion: do not trust your eyes or brain to show you what is really there!