Scanning for photo-worthy organisms, you spot a flash of blue: a flower? a bug?
It’s reflecting wavelengths of blue light back to your eyes – thus the brilliant color. But how does that happen? Surprisingly, there are two very different ways to get a biological blue, one due to chemistry and the other to physics.
PIGMENTS: Better color through chemistry.
Due to their chemical structure, pigment molecules absorb some wavelengths of light and reflect others. Those wavelengths reflected are the color you see. Because the color is caused by molecules, as long as they’re around, you have color and it looks the same regardless of what angle you view it from. Thus, a blue Bachelor’s Button flower looks blue from all angles. If you picked it and ran it through a blender (don’t try this at home), the resulting gory paste would still be blue.
Most blues seen in flowers and fruits come from anthocyanin pigments. Animals generally don’t make anthocyanins, so blue-pigmented animals are uncommon, but there’s another option…
STRUCTURAL COLORS: Gorgeous hues from physics.
Structural colors are caused by light reflected off the textured surfaces of objects or the interior structures of transparent cells. They aren’t due to the chemical structures of individual molecules, but to the shapes those molecules are organized into. Structural colors often look iridescent, and viewing angle affects your orientation to the “reflectors”, so whether you see color and what color you see can vary. (Think of how a ruby-throated hummingbird’s red patch glows ruby from some angles and looks black from others). Peacock feathers and blue tarantulas owe their blues to structural color. Thus, if you tossed a peacock feather in a blender (don’t try this at home) and ground it into dust, the blue would vanish and you’d be left with brownish dust. No structure, no blue.
Animal blues are commonly due to structural colors (ex. Morpho butterflies and Blue Jays), but it’s less common in plants. However, some shade-adapted leaves (ex. Begonia sp.) and occasional fruits or flowers do owe their blue sheen to structural color rather than anthocyanins.
