Multiple Structural Coloring of Silk‐Fibroin Photonic Crystals and Humidity‐Responsive Color Sensing

In the biological world, numerous creatures such as butterflies, insects, and birds have exploited photonic structures to produce bicolor reflections with important biofunctions in addition to unique brilliant structural coloration. Although the mimicking of bistructural color reflection is possible, the fabrication involves a process of combined layer deposition techniques, which is complicated and less flexible. Here, a bistructural color mimicking, based on silk fibroin, is reported using a simple and inexpensive self‐assembly method. Silk‐fibroin inverse opals with different spectral positions of bistructural color reflection (i.e., ultraviolet and visible peaks, ultraviolet and near infrared peaks, and visible and near infrared peaks) are obtained by simply controlling their lattice constants. Furthermore, the inline and continuous tuning of the peak positions of bistructural color reflection can be achieved by the humidity‐induced cyclic contraction of silk fibroin. The potential applications of silk‐fibroin photonic structures in eco‐dying and multifunctional silk fabrics are also demonstrated.