The blue and green swirls “illusion” is misleading and the implication that there isn’t any blue in the picture is just plain out wrong. Yes, the center of each stripe is the same light green color: RGB( 0, 255, 150).
The reason the blue swirls look like blue swirls is not only because there is some psychological trick of the brain. IT’S BECAUSE THEY’RE BORDERED BY ACTUAL BLUE PIXELS. The reason the green one looks green is BECAUSE IT’S BORDERED BY DARKER GREEN PIXELS. Here’s an extreme closeup of the ORIGINAL graphic illusion.
I mean… for the smaller part of the swirl, the pixels are almost completely blue or completely dark green! Are you kidding me?! Come on Internet! You can do better than this!
Despite this, the original concept is sound. With straight lines, the real optical illusion effect seems to hold up or at least be unsullied by pixelation. You can see a more accurate example of the illusion here. Why no one is sharing this version around the interwebs, I can’t say.
The constant repeating, reblogging and resizing to pass on this “WONDER OF SCIENCE” (waves hands appropriately) has turned it into something that smacks of inaccuracy rather than the really cool optical illusion it should be. The dude who originally made this famouser was the guy from Bad Astronomy. The second example on his post is MUCH more accurate pixel-wise than the original swirl. However, even if you resize the more accurate second image, it pixelates and your monitor will actually add blue pixels to the image. (Try hitting your Control and minus/hyphen key and see!)
::throws hands up::
So, to conclude, this color illusion does work! However, the “green swirl” image being shared around really does have blue in it.
If you’re interested in more color illusions, this is a good site that explains how they’re created.
TGNP: Campaigning for Internet Accuracy