The bright colors of some butterflies, beetles or birds are not due to the presence of pigments that selectively absorb light, but due to the so-called structural coloration. Structural coloration occurs on surfaces with a nanostructure with dimensions similar to those of the wavelength of the incident light (typically below the micron). These ordered nanostructures are known as photonic crystals. There is a great interest in providing cellulose, the most abundant polymer in earth, biocompatible and biogradable, with these structures, which can offer new optical and electric functionalities.