See that red box above? It’s an “anti-colorblindness” test: It contains an image that only the colorblind can see. Aaron Clauset developed the idea and designed a few images that you can check out on his web site; as he notes …

If it’s painfully obvious that there’s another image there, then you’re probably colorblind to some degree in the red part of the spectrum. Can’t see it? Try looking at the white space at either side of the image, you might be able to see the object by using your contrast-sensitive rods (which are concentrated more heavily in your peripheral vision). Don’t give up if you can’t see it, that’s the whole point — this is an *anti* colorblind test.

I love this idea: A way of regarding colorblindness so that it is a special ability, not a visual handicap. Keep in mind that my replication of his “red” test above has it shrunk down to half-size; the effect probably doesn’t work unless you go look at the original test at full size here. He also shows the solutions here, in case you’re still scratching your head wondering what secret the pictures contain.

(Thanks to Reddit for this one!)