Fig. 1. Chemical and structural colors in nature. (a) Chemical structure of chlorophyll a and its chromophore chlorin, along with the absorption spectra of chlorophylls a and b in dichloromethane solution^[2]. (b) SEM image of nanostructures on the surface of chameleon skin and its color variation^[10].

Fig. 2. Physical model for producing structural color. (a) Electric dipole response of single metal nanosphere; schematic representation of color response of blue, green, and red achieved by arrays of metal nanodisks of different sizes and periods; model of metasurface achieving gap plasmonic mode. (b) Magnetic dipole response of a single dielectric nanodisk; schematic representation of the color response of blue, green, and red achieved by arrays of dielectric nanodisks of different sizes and periods; schematic representation of a metasurface capable of generating BIC modes.

Fig. 3. Early designs of structural colors based on metal nanostructures. (a) Reflective structural color achieved with an array of Ag nanorods, requiring only a 2×2 array for distinguishable pixels^[42]. (b) Anisotropic cross-shaped nanoapertures for polarization-sensitive transmissive structural color^[99].

Fig. 4. Plasmonic structural color design for high-performance display. (a) Design using Ag nanorods for high-color saturation display (1), brightness control by adjusting nanorod size (2), and color tuning through the arrangement of structures with different wavelength responses (3)^[101]. (b) Schematic of high-performance structural color based on Ag nano-grooves for achieving complete control over brightness and color (1), (2), application of polarization response for advanced optical steganography (3), and achieving soft color displays through brightness variation (4)^[102].

Fig. 5. Structural color design based on FP cavity. (a) Integration of Si nanostructures into FP cavity for uniform cavity length structural color display (1), color tuning through the mixture of different nanostructures on a high-color-saturation display foundation (2), and easy achievement of polarization response by controlling the symmetry of nanostructures (3)^[109]. (b) Schematic structure of FROCs formed by two coupled light absorbers (1), deposition of an absorbing medium on the FP cavity, coupling of the upper broadband mode with the lower FP resonance to form Fano resonance, resulting in vivid structural colors (2), (4), and exhibiting over 50° observation angle (3)^[110].

Fig. 6. Designs based on plasmonic resonances in the gap plasmon. (a) Schematic of gap plasmonic structure based on aluminum nanorods (1), and achieving structural color pixels with a single nanostructure and black pixels by blending different nanostructures (2)^[113]. (b) Process flow and structural schematic of large-scale preparation of Ag nanorod gap plasmonic structures using colloid lithography, along with samples and characteristics in CMY mode—cyan, magenta, and yellow (2)^[114].

Fig. 7. Structural color design based on Si. (a) Si nanorod array on a sapphire substrate, introducing PMMA and DMSO as refractive index matching layers for high-performance structural color (1), reflection spectra, and CIE coordinates of the sample (2), (3), displaying a vivid phoenix pattern (4)^[138]. (b) Preparation of different-sized air holes on Si surface, localizing the electric field in the air, achieving Mie resonance structural color at short wavelengths, with reflection spectra and electric field decomposition as hole size varies (1)–(3)^[139]. (c) Schematic of high-saturation red design based on Si nanoantenna array BIC mode (1), simulation and actual reflection spectra, and corresponding CIE coordinates (2), (3), (5), Ez electric field components for both modes (4), and SEM image of the actual sample (6)^[140].

Fig. 8. Structural color design based on TiO2. (a) Design of trapezoidal TiO2 nanorod array structural color (1), (2), reflection spectra, and CIE coordinates for different sizes (3), (4)^[134]. (b) Schematic of structural color based on multi-layer dielectric nanorods (1), reflection spectra covering the entire color space (2), and Mie decomposition for any structure proving suppression of higher-order modes by multi-layer dielectric structures (3), (4)^[152].

Fig. 9. Design of metasurfaces using DNN. (a) General flowchart of metasurface design using DNN^[171]. (b) Reinforcement learning is applied to the design of an all-dielectric structural color. The structure model based on Si and the training process (1); ML training results achieve higher color saturation compared to previous human-designed structures (2)^[172]. (c) Training and spectral prediction of TiO2 grating structure using MVANN. Training model and training process for the four parameters of the structure and their corresponding spectra (1). (2) Color gamut distribution after network optimization, where arrows indicate the colors corresponding to the spectra in (3)^[173].

Fig. 10. Various design methods for achieving dynamic structural colors are illustrated. (a) Dynamic structural color achieved through voltage-driven ion injection^[175]. (b) Erasable structural color based on a reversible hydrogenation-oxidation process^[176]. (c) Dynamic structural color achieved through microfluidic control^[177]. (d) Brightness-changing structural color based on polarization^[178].

Fig. 11. Dynamic structural color design based on VO₂ and GST phase change materials. (a) VO₂ as a tunable dielectric spacer in MIM structure (1), and absorption and color changes before and after phase transition (2), (3)^[212]. (b) Dynamic structural color design based on GST, schematic of dynamic film and pixel tunable display structure (1), (2), structural colors with different film thicknesses (3), and schematic of flexible transparent display sample (4)^[215].

Fig. 12. Dynamic structural color design based on Sb2S3. (a) Mie resonance structural model based on Sb2S3 nanorods (1), reflection spectra changes before and after phase transition (2), and Mie decomposition (3)^[217]. (b) Dynamic tunable FP resonance mode based on Sb2S3 (1), continuous color change achieved by controlling intermediate states of Sb2S3 phase transition, enabling multilevel adjustment of refractive index (2), (3)^[218].

Fig. 13. Dynamic structural color adjustment using liquid crystal and polarization-sensitive metasurfaces. (a) Anisotropic Al nanoholes integrated with LC for switchable structural color display (1), and voltage-induced modulation of transmission intensity with a switch time on the order of milliseconds (2)^[224]. (b) Elliptical Mie resonators integrated with LC for brightness-adjustable dynamic color display (1), continuous changes in RGB color brightness under different polarizations (2), and dynamic color display of actual samples with increasing voltage (3)^[225].

Fig. 14. Dynamic structural color based on mechanical stress-induced structural changes. (a) Voltage-tunable FP resonance mode, adjusting grating structure height with changing voltage (1), (2), lowering height to induce resonance wavelength changes, and achieving color changes (3), (4)^[228]. (b) TiO₂ nanostructure array prepared on a flexible substrate (1), and dynamic adjustment of structural color by applying external stress (2)^[229]. (c) Kirigami grating structure prepared via nanoimprinting and laser etching (1), grating structure exhibiting strong selectivity for observation angle (2), and dynamic structural color display achieved by applying external force or combining with a drive motor (3), (4)^[230]. (d) Composite of ATO nanoparticles and mechanically responsive color-changing pigment in a highly elastic liquid crystal substrate (1), achieving dynamic color changes with high saturation and a wide color gamut (2), (3)^[231].

Fig. 15. Applications of structural color in the display. (a) Voltage-driven in-situ color-changing multilayer film structure (1), (2), initial colors of different thicknesses of Fe2O3 layers (3), and reversible color changes under positive and negative bias (4)^[188]. (b) High-resolution OLED design based on structural color surfaces (1), controlling FP mode by adjusting OLED layer thickness (2), achieving higher brightness at the same power due to reduced optical losses of traditional color filters, and maintaining good color display even with a minimum subpixel structure of 1.2 µm (3), (4)^[238]. (c) Combining color filters with micro lenses to achieve 3D structural color display is illustrated. Schematic diagram of 3D display achieved through diffuse light (1). SEM images of the display unit and a 3 pixel × 3 pixel unit, where each pixel consists of 5×5 nanopillars (2)^[241].

Fig. 16. Applications of structural color in optical encryption. (a) Advanced optical encryption design combining orbital angular momentum (OAM). SEM image of a single CVB unit (1). Individual control of color and OAM information on a single surface (2). Optical decryption process based on physical keys (3)^[250]. (b) Laser-induced volcano-like nanostructures on MIM surfaces (1), volcano structures showing significant angular anisotropy (2), precise control of nanostructure size by adjusting laser power (3), and utilizing volcano-like nanostructures for advanced optical steganography (4)^[251].

Fig. 17. Applications of structural color in the field of multiple information. (a) Metasurface enabling both structural color and holographic display of multiple information (1), multiple nanostructures forming a unit cell, modulation of holographic image information through integrated LC (2), and combining structural color with voltage-driven holographic images for multiple information transfer and advanced optical encryption (3)^[262]. (b) 3D integrated metasurface for high-performance multifunctional displays. Metasurface structure shiyitu1 and SEM image (1). Simulation design and actual structural color with holographic images (2)^[263].

Fig. 18. Applications of structural color in coatings and ink fields. (a) Preparation of ink with mixed silica nanoparticles for printing, removing excess liquid phase by heat treatment (1), and easy adjustment of ink color by changing nanoparticle diameter (2)^[269]. (b) Self-assembled Al nanoparticles on alumina surfaces for creating plasmas used in the preparation of super-light coatings (1), due to the isotropic nature of self-assembled particles, exhibiting polarization- and angle-insensitive properties (2), controlling color by adjusting the deposition time of Al atoms (3), and preparation of super-light coatings with only 0.4 g/m² in organic solvents (4)^[87].

Fig. 19. Applications of structural color in the field of biosensors. (a) Cellular color observation based on structural color of metal metasurfaces. Biological slice model based on nanoslides, and two different designs of metasurface models (1). Testing with nanoslides for different thicknesses of Pt/C, showing significant color differences for 3, 8, 13, and 19 nm, achieving a resolution of over 3 nm (2)^[289]. (b) Plasmonic structure based on M13 bacteriophage as a biological medium for lung cancer detection (1), validation of color array for quantitative and qualitative analysis of different organic compounds (2), and combining DNN training to achieve 90% accuracy in disease diagnosis (3)^[290].

Fig. 20. Achieving large-scale structural color production based on nanoimprinting and 3D printing. (a) Structural color technology based on nanoimprinting. Schematic representation of large-area pattern transfer using nanoimprint stamps (1)^[100]. Large-area and rapid preparation using roll-to-roll nanoimprint (2)^[307]. (b) structural color technology based on 3D printing. Grating structure achieved by direct inkjet printing (1)^[313]. Structural color 3D printing using resin with composite nanoparticles (2)^[314]. Preparation of metasurface structural color based on two-photon polymerization (3)^[316].