Photonic crystals have been found to play a significant role in many biological systems, but perhaps none as beautiful as in the male beetle Hoplia coerulea, which is found in southern Europe. Jean Pol Vigneron and colleagues of the University of Namur in Belgium have shown that this little fellow owes his striking blue coloration to a 3D photonic crystal structure made of multiple layers of dielectric biological material.
In detail, the structure discovered involves layers of thin plates alternating with rows of parallel rods. This results in a change in the reflected light from blue to violet as the angle of incidence becomes larger. The structure could lend itself to commercial fabrication, albeit not without some effort.
Further reading
Jean Pol Vigneron et al. 2005 Phys. Rev. E 72 061904.