Interesting here is: Actually, for most blue butterflies, it’s not even a pigment-it’s just a trick of the light.
Since blue is so rare in the biological world (hardly any plants or animals can produce real blue chemicals), they evolved structural colors.
Their wings have these microscopic ridges that reflect blue light while canceling out other colors.
It’s basically the same reason the sky looks blue, just built into a wing. If you were to look at the wings from a different angle or get them wet, the blue often disappears because you're messing with that physical structure
Not just butterflies, birds too! But what selection pressure drove the evolution of these structural colors? Presumably signaling, the opposite of muted, camouflaging colors.
Also, as many might know, blue eyes are the result of a lack of pigment (eumelanin). The iris is translucent, but Rayleigh scattering preferentially backscatters blue photons. Green eyes have some pigment, making them a mix of brown and blue.
Inventions can be useful recombinations or applications of other inventions. They don't need to be wholly unique unto themselves. Indeed, the vast majority of them are not wholly unique.
It’s basically the same reason the sky looks blue, just built into a wing. If you were to look at the wings from a different angle or get them wet, the blue often disappears because you're messing with that physical structure