The irridescent blue seen in this macrophoto of a Morpho Rhetenor butterfly is due to structural colour – not  pigment.  The butterfly’s wing scales have microstructure which act like a specialised diffraction grating, so it is an interference/diffraction grating effect that gives the striking blue colour – visible over a wide range of angles.  It is in fact an example of a natural photonic crystal structure – something that I researched for a few years at the University of Southampton.  Possibly one of the most impressive Icons of Science meeting Art 🙂

See my 20-page Review Article titled “Biomimetically Inspired Photonic Nanomaterials” for more information.