Let us dive into the sea, beyond the colorful world of the sun. About 1,000 to 2,000 feet down, we’ll arrive at a place where only blue beams in sunlight can penetrate. This is the home of the swell shark and chain catshark. Look at them with your human, land-ready eyes, and all you’ll see are a couple of unimpressive fish, spotted in shades of brown, beige and gray.

But peer through a blue filter, more like the way these sharks see each other, and behold beaming beauties robed in fluorescent green spots.

Recently scientists discovered that these sharks see the world totally differently than we do. They’re mostly colorblind, with eyes that can detect only the blue-green spectrum. This means when the sharks appear to change color in the blue water, they’re almost projecting a secret code to other sharks: One pattern male, the other female — come and get it. But just how they take blue light from their dull environment and transform it into a neon sign has been a mystery.