So do you think (A) and (B) are different colors?

It looks that way doesn’t it?   Well they are the exact same shade of grey.  Don’t believe me?   Cut and paste this image into MS Paint, and then cut the (A) and (B) squares out, and put them side by side.

It’s an example of the way your eye will fool you when looking at shades.  I discovered this on this website here.

And here is a cool little 20 second demo on the “simultaneous contrast effect.”