LAUSR

Structural colors arising from interactions of light with submicron scale periodic structures have been found in nature. Inspired by photonic materials, rewritable paper using water as ink is fabricated via entrapping amorphous colloids crystals film into hydrogel. This photonic paper is tough, free‐standing, transparent, and colorless in dry state, just like plastic sheet. Marks display using water as ink to write on the paper and disappear with the evaporation of water. The color of the marks similar to that of the initial PS colloids film and could be tuned by changing the size of the colloids. The photonic paper possesses high durability and can be rewritten over 70 cycles without significant color fading. Besides, the retention time of the written marks could be well controlled from minutes to weeks by using glycerol/water as ink. It is worth noting that long‐range order is not the necessary condition for the formation of photonic paper, which makes the preparation easy to achieve. More interesting, the wet hydrogel film is sensitive to strain, and has the potential to be mechanical sensor.