This is another one of those illusions that is so strong, so powerful, that you won’t believe me until you actually take two pieces of paper, or your hands and cover up part of the screen.
Here’s what you should do: First, notice that the upper left shade of red looks much lighter than the shade of red in the lower right corner. Actually, this is NOT TRUE! The red is exactly the same shade. Second, to prove my point, cover up the top three “letters” with one hand, and the letter on the bottom with your other hand. Yes, that’s exactly the same shade of red.
How does this optical illusion work? As you have probably guessed, it’s because of the black and white outlines in the characters. When you put white next to any color, it will bring out the lighter characteristics of that color, as you can see in the example above. The same is true with black, the more black next to something, the more that the black will cause us to perceive the colors around it as darker.