Synergistic Movement of the Dual‐Layer Photonic Guanine Crystal Arrays Reveals a Mechanism of Light Stimuli‐Responsive Structural Color Change in the Zebrafish Skin

Light stimuli-responsive structural color change is ubiquitous in animals, serving functions such as camouflage and social signaling. The striped pattern of zebrafish changes from slate-blue in dark-adapted conditions to bright-blue in light-adapted conditions. Our study reveals that this reversible color variation originates from the synergistic movement of the dual-layer guanine reflector. This reflector is composed of inclined crystal arrays in S-iridophores and horizontal crystal arrays in L-iridophores. The classical "Venetian blind" model, which relies on a single-layer photonic crystal array and emphasizes the influence of individual structural parameters like the tilting angle, failed to predict structural color change in the zebrafish skin. However, this color variation could be well described by our "Dragon Boat" model, which considers the synergistic movement of the dual-layer photonic crystal ultrastructure. Key findings in our study show that the reflectance peak position is controlled by crystal tilting angles and spacings, while its intensity depends on interlayer distance. These new insights offer a framework for designing biocompatible optical materials with tunable light properties.