Color Square Illusion

I saw this on the web and the description said that squares A and B were the same color. I thought it was a misprint as I knew that those two squares were not the same color.

I squinted. I moved across the room. I looked at it from extreme angles. I held up two strips of paper on my screen to block out the green rod and the other squares. They still looked like two different shades. I knew that those two colors were not the same.

I decided I would prove it and send a comment exposing this as an evil sham designed to strain the eyes of the unwary. I downloaded the picture from the site and opened it up in Photoshop.

• Test One: Using the eyedropper tool I captured the hex color in each square. They were the same. I didn't believe it and did it again. Repeatedly. I found a slight variation in a few stray pixels, but for all practical purposes they were the same.
• Test Two: Using the lasso tool, I captured a segment of square A and then pasted it into it's own layer. I then moved the square back and forth between the two squares. Freaky! It seemed to change color as I moved it.
  
• Test Three: Using the lasso tool, I captured a segment of each square and pasted them onto their own layer. Then I hid the original picture and moved the two squares side by side. Without the original picture, they looked the same. My convictions were getting pretty shaky by now.
• Test Four: I grabbed the color from square A and using the brush tool I painted the area between the two squares the same color. As I did this, suddenly, I could see they were the same. I no longer believe what I see.
  

I read the explanation on the site and it didn't make sense to me. In the comments section an anonymous poster wrote this:

"In the real world, this wouldn't be the same grey, as B square is in the shadow of the column, so our smart brain corrects what it receives from the eye and optic nerve, and tells us that B square "must" (should?) be lighter than A square."

That explanation makes a bit more sense to me than the more technical one on the site. Either way it is a fascinating illusion.

Update: Visited the original site today and they've added a couple of graphics that help you see that the two squares are the same. Must of had a bunch of non-believers write to say, "No way!"

[Image: Captured from Might Optical Illusions: http://www.moillusions.com/2006/03/colored-squares-illusion.html]