Sharks aren't blue because of skin pigment—they actually have millions of tiny mirrors built into their skin.
arXiv · March 17, 2026 · 2603.13937
The Takeaway
Unlike almost all other vertebrates that use cells or pigments for color, blue sharks have evolved a 'photonic architecture' inside their skin scales. These scales act like tiny optical pixels, using organized crystal stacks to bounce back specific wavelengths of light to hide the shark in the open ocean.
From the abstract
The blue shark (Prionace glauca) exhibits a striking dorsoventral color gradient, transitioning from vibrant blue dorsally to silver and white ventrally, a pattern widely interpreted as pelagic countershading. Despite its ecological significance, the physical basis of this coloration remains unresolved. Here we show that this color system does not arise from dermal chromatophores, as in most vertebrates, but from a previously unrecognised photonic architecture housed within the pulp cavity of in