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DOI: 10.1002/adma. 201603560 can be at the origin of the cellulosic solid films’ colors, which also varies with the viewing angle. Usually the solid films are prepared from isotropic or anisotropic suspensions of CNCs in water. The optical properties of the films were found to depend upon the characteristics of the colloidal suspensions, which pass through different stages upon solvent evaporation and before the formation of the film. In order to use these films for optical applications, many attempts have been undertaken to control their optical properties and mainly their reflection characteristics.[6–9] If casting followed by a slow solvent-evaporation method [4, 8, 10] is used, the resulting films show iridescent colors and its cross-sections can present several domains with different pitch values. It has been found that the films’ surface can have planar alignment over long distances, compared with the cellulose rods’ lengths.[4] However, the film’s reflection peaks have broad widths indicating the presence of several pitch values, which should come from the cholesteric layers within the films.[11] The existence of grooves between aligned layers has also been recently described in the literature.[12] It seems that the evaporation of the water dictates the internal structure of the films, allowing the formation of several layers with different thicknesses and pitches.[10] Some works have been devoted to avoid these defects.[8] Other photonic structures that reflect both RCP and LCP light can be found in nature, as for example in the cuticle of Plusiotis resplendens.[13] The appearance of the insect is the result of a selective color reflection from a structure existing in …