Same color illusion

Here's a quick hit. I originally wanted to talk about the concept of saccadic masking, but as I am not an expert on our visual system, I would have probably quoted the Wikipedia page verbatim. So, I'll go with one of my favorite optical illusions, the same color illusion.

Look at the image above. There are two squares (parallelograms, really, but close enough) labeled A and B. Look at the colors of the squares that the letters rest in. (I often have people get confused and think they are supposed to look at the colors of the letters. Don't.)

Is there any difference between colors of the squares?

To me, it seems like square B is lighter than square A, as we can use all of our context clues to infer as such: The board is checkered, with the main diagonals a lighter colored gray than the other squares. Square B is a bit darker than some of the other squares on the diagonal, but that's because it is in the shadow of the green cylinder. So where's the illusion?

Try doing this: instead of focusing on the two squares, look at the white space around the checkerboard. Let your peripheral vision take in the two labeled squares. Do you see the curtain being pulled back now? Or are you still not convinced there is an illusion?

Here is a guaranteed way to solve this mystery.

• If you have an image editing software on your computer (if all else fails, use Microsoft Paint), save this image and load it into your editing program.
• There should be a tool somewhere in the program that looks like an eyedropper. This tool takes a color from an image and makes it your primary color for use with your other editing tools (like the paintbrush, for example).
• Take your eyedropper and select the color of square A by hovering over the square and left clicking.
• Then, switch to your paintbrush and paint a little circle somewhere in the white space of the image.
• Next, take your eyedropper and select the white space around the checkerboard.
• Then, still using the eyedropper, select the color of square B.
• Finally, switch to your paintbrush tool again and paint a little circle right next to the previous circle you just created from the color of square A. Overlap the colors if you want.

The illusion is revealed. Both square A and square B are the exact same color! Is it a trick with the image? Are they not actually the same color, but my methods of seeing the illusions created a false sense that they are the same? There is a trick, but it's one you are playing on yourself.

From what I can understand from the reading I have done on this illusion (not to mention a few wild guesses), your eyes and minds inability to cope with the pseudo-three-dimension of the image is your downfall. Instead of understanding that you are actually looking at a flat image with colors that are not affected by light and shadow, your mind uses what it knows about three dimensional imagery and lighting and convinces your perception that it needs to follow a set of rules, which could be:

• The board is checkered with an alternating pattern of a light square bordered on all sides by dark squares, and vice versa.
• The green cylinder is casting a shadow over square B and a few adjacent squares, so these colors are darker, but still maintain the pattern above.

If we were to have an image of square B as a light square, but surrounded in all direction - including top left, top right, bottom left, and bottom right, as well as decrease the size of the shadow so it only fully covered square B, then the top left and bottom right squares, unaffected by the shadow, should immediately look the same color as square B.

You have any optical illusions that you find fascinating or mind-blowing?