Noniridescent Structural Colors Research Articles

Spontaneous Photonic Jammed Packing of Core-Shell Colloids in Conductive Aqueous Inks for Non-Iridescent Structural Coloration.

Integrating structural colors and conductivity into aqueous inks has the potential to revolutionize wearable electronics, providing flexibility, sustainability, and artistic appeal to electronic components. This study aims to introduce bioinspired color engineering to conductive aqueous inks. Our self-assembly approach involves mixing poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with sulfonic acid-modified polystyrene (sPS) colloids to generate non-iridescent structural colors in the inks. This spontaneous structural coloration occurs because PEDOT:PSS and sPS colloids can self-assemble into core-shell structures and reversibly cluster into photonic aggregates of maximally random jammed packing within the aqueous environment, as demonstrated by small-angle X-ray scattering. Dissipative particle dynamics simulation confirms that the self-assembly aggregation of PEDOT:PSS chains and sPS colloids can be manipulated by the polymer-colloid interactions. Utilizing the finite-difference time-domain method, we demonstrate that the photonic aggregates of the core-shell colloids achieve close to maximum jammed packing, making them suitable for producing vivid structural colors. These versatile conductive inks offer adjustable color saturation and conductivity, with conductivity levels reaching 36 S cm-1 through the addition of polyethylene glycol oligomer, while enhanced water resistance and mechanical stability are achieved by doping with a cross-linker, poly(ethylene glycol) diglycidyl ether. With these unique features, the inks can create flexible, patterned circuits through processes like coating, writing, and dyeing on large areas, providing eco-friendly, visually appealing colors for customizable, stylish, comfortable, and wearable electronic devices.

Bio-inspired stretchable and self-healable nanocomposite gelatin hydrogel with low silica nanoparticle content and brilliant angle/strain-independent structural colors

Stretchable and self-healable structural-colored nanocomposite gelatin hydrogel with photonic structure of random dense/loose regions of non-close-packed silica nanoparticles (SiO2 NPs) is developed via convenient and scalable polymer-mediated assembly. The formation of the special photonic structure with overall low SiO2 NP content is characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The small-angle X-ray scattering test indicates the existence of short-range order, which is consistent with the TEM and SEM results. The dense photonic structure consisting of SiO2 NP chains and domains, and the loose structure consisting of abundant solitary SiO2 NPs, accounts for pronounced and uniform structural colors via combined effects of coherent scattering of light by dense structure, and Mie scattering of solitary NPs. These structural colors are independent of viewing angles and large mechanical strains. The dynamic physical and chemical bonding of the gelatin hydrogel network matrix enables self-healing functions and good deformability. Moreover, salt treatment of the structural-colored gelatin hydrogel networks enhances physical crosslinking and the mechanical strength of the hydrogel. The resilient, flexible and self-healable structural-colored nanocomposite hydrogel with low SiO2 NP content has great potential in wearable photonics, cosmetics, and various other color-related fields. This work also sheds light on enhancing non-iridescent structural colors through advanced photonic design.

Transcriptome and proteome revealed the differences in 3 colors of earlobe in Jiangshan Black-bone chicken

The earlobe is a featherless, exposed thickening located beneath the ear canal of chickens, which plays a visual signaling role in age, performance, mental vitality, reproduction, and other aspects. However, despite its importance, there have been few studies on the color differences and formation mechanisms of chicken earlobes, particularly the structurally blue earlobes characteristic of the Jiangshan black-bone chicken. In this study, we explored the physiological mechanisms that may influence the formation of differently colored earlobes using 3 types of earlobes from Jiangshan black-bone chickens: light peacock green (Green group), dark peacock green (Blue group), and dark reddish purple (Black group). All 3 earlobe colors exhibited positive melanin Masson-Fontana staining, and the thickness of collagen fibers in the dermis decreased in the order of Green, Blue, and Black groups. A total of 1,953 differentially expressed genes (DEGs) were detected in the 3 earlobes through mRNA sequencing, among which the GO term "collagen trimer" was significantly enriched in DEGs between groups. Additionally, 716 differentially expressed proteins (DEPs) were identified in the 3 earlobes using 4D-DIA proteomics, with the term "collagen fibril organization" being significantly enriched in DEPs between the Green and Black groups. Integrated analysis of transcriptome and proteome data revealed that 12 DEGs and DEPs were commonly differentially expressed between the Green and Black groups, including the gene LUM (corneal keratan sulfate proteoglycan), which was significantly enriched in the "collagen fibril organization" GO term. In conclusion, our study suggests that LUM plays a crucial role in the formation of peacock green earlobes in Jiangshan black-bone chickens. The high level of LUM in peacock green (Green and Blue groups) may affect collagen nanostructures, leading to a stronger effect of melanin-supported dermal collagen on the production of non-iridescent structural colors through coherent scattering, resulting in a bright structural blue color in Jiangshan black-bone chickens. In contrast, the low expression of LUM in dark reddish purple (Black group) reduces the reflection of non-iridescent structural colors, making the earlobe color appear almost black, similar to melanin.

Achieving High-Temperature Stable Structural Color through Nanostructuring in Polymer-Derived Ceramics.

Structural colors offer a myriad of advantages over conventional pigment-based colors, which often rely on toxic chemical substances that are prone to UV degradation. To take advantage of these benefits in demanding environments, there is growing interest in producing structural colors from ceramics. Polymer-derived ceramics (PDCs) emerge as a compelling choice, presenting two distinct advantages: their enhanced shape ability in their polymeric state associated with impressive temperature resistance once converted to ceramics. This study pioneers the fabrication of noniridescent structural colors from silicon oxycarbide (SiOC) PDC, enabled by the nanostructuring of an inverse photonic glass within the PDC material. This design, a functionally graded material with an inverse photonic glass (FGM-PhG) structure, leverages the innate light-absorbing properties of SiOC, yielding a vivid structural color that maintains its saturation even in white surroundings. This study elucidates the process-structure-properties relationship for the obtained structural colors by investigating each layer of the functionally graded material (FGM) in a stepwise coating deposition process. To further emphasize the exceptional processing flexibility of PDCs, the three-step process is later transferred to an additive manufacturing approach. Finally, the FGM-PhG structural colors are demonstrated to have remarkable thermal stability up to 1000 °C for 100 h, possibly making them the most thermally stable ceramic structural colors to date.

Bio-inspired fabrication of non-iridescent structural color coatings with excellent colorfastness for rapid and large-scale colorization of textile

Structural color in nature provides a new strategy for eco-friendly colorization. Biomimetic construction of amorphous photonic crystals (APCs) on the substrate surface can form a specific non-iridescent structural color, which can be widely used in textile, paint and other fields. However, the APCs structural color has the shortcomings of dim color and poor colorfastness, which restrict the industrial application. In this study, base on the structural design of APCs building blocks, a novel copolymer containing reactive epoxy groups of poly (styrene-co-glycidyl methacrylate) (P(St-co-GMA)) was synthesized, which was used for fabricating APCs structural color by rapid spray coating method. P(St-co-GMA) nanospheres with different particle diameters can be self-assembled into APCs showing different crack-free structural colors. This research reports for the first time that the polymer nanospheres with two different particle diameters were synthesized by one-pot polymerization to enhance the color brightness of structural color. P(St-co-GMA) nanospheres structural colorized fabrics showed excellent colorfastness, flexibility and air permeability. This research promotes the industrial application of structural color for the rapid larger-scale fabrication of APCs with excellent colorfastness on substrates through the synthesis of polymer nanospheres with reactive epoxy groups.

Non-iridescent magnetite photonic crystal films and pigments with enhanced magnetic coupling effect

Non-iridescent structural color films and pigments with novel enhanced microwave absorption characteristics are successfully fabricated at room temperature for the first time. The quasi-uniform magnetite nanoparticles (CV = 0.10 ∼ 0.20) with high refractive index (n = 2.42) and broad light absorption provide evident low-angle-independent property for the structural color pigments. More importantly, a universal technical protocol is developed for preparation of photonic crystals with inorganic nanoparticles, i.e., through designing of the binding strength between nanoparticles and mediated molecules, the slurry modulus is increased to 105 Pa, which effectively drives the nanoparticles to rapidly assemble into closely packed ordered arrays by our-designed powerful assembly technique. Additionally, the structural color materials are subjected as photonic crystal pigments (∼20 wt%) embedding in a transparent polymer matrix to form color coatings. Remarkably, the photonic crystal pigments exhibit strong magnetic coupling effect and enhanced microwave absorption performance due to the regular arrangement, with superior reflection loss (RLmin) values of −14.97 dB (increase by 65.8 % compared with randomized magnetic nanoparticles), and the effective absorption bandwidth (EAB) of 2.15 GHz. This new kind of photonic crystal pigment, combining visual color and radar wave absorption, provides a novel idea for developing of multi-wave-band high-performance stealth materials.

Achieving saturated non-iridescent structural colors via island-like polypyrrole coating on SiO2 microspheres and enhancing their stability through a melt-curing strategy

Structural colors with high saturation and high stability.

Waterborne Polymer Coatings with Bright Noniridescent Structural Colors.

Structural color pigments offer an efficient, sustainable, and environmentally friendly approach to obtain waterborne polymer coatings. We developed polymer-based spherical photonic pigments to incorporate in aqueous dispersions of polymer nanoparticles used to obtain waterborne polymer films. Our spherical photonic pigments are assembled from polymer nanoparticles and are highly stable in water dispersion, maintaining their optical properties in the final polymer films. Unlike conventional dyes and pigments, which are prone to photobleaching because they are based on the absorption of light, photonic pigments rely on the selective reflection of light by their nanostructure and therefore are not photodegraded. Furthermore, different colors can be obtained from the same materials, changing only their nanostructure, in this case, the size of the polymer nanoparticles. Our novel spherical photonic pigments are noniridescent and can be incorporated in aqueous polymer nanoparticle dispersions without deteriorating their structure to produce waterborne polymer coatings with structural color. This approach for structural colored waterborne polymer coatings is efficient, simple, and environmentally friendly, offering excellent prospects for application in paints and coatings.

Colored textiles based on noniridescent structural color of ZnS@SiO2 colloidal crystals for daytime passive radiative cooling

Passive radiative cooling (PRC) technology, which utilizes the optical properties of materials to achieve electricity-free and spontaneous cooling, holds great promise for energy conservation and combating global warming. Integrating PRC with textiles enables precise regulation of the microclimate of the human body, facilitating sustainable and effective individual thermal comfort. However, such PRC materials typically exhibit a white or mirror-like appearance to minimize solar energy absorption, severely limiting their aesthetic appeal and practical application in real-life scenarios. Herein, we present a colored textile for PRC by employing the spray coating method with noniridescent structural color pigments consisting of carbon-modified ZnS@SiO2 core–shell microspheres (colloidal crystals). This approach simultaneously achieves noniridescent colors and efficient cooling. By using the photonic properties of ZnS and the core–shell structure, the ZnS@SiO2 colored textile selectively reflects visible light, resulting in coloration while reducing solar absorption. Furthermore, the phonon resonance (Fröhlich mode) of the SiO2 shell ensures high emissivity of the ZnS@SiO2 colored textile within the atmospheric window, allowing for substantial radiative heat dissipation. Outdoor experiments demonstrate that both the green and amaranth ZnS@SiO2 textiles could lower the simulated skin temperature by 5 ∼ 6 ℃ in direct sunlight, compared to ZnS and dye textiles of the same hue. Additionally, the ZnS@SiO2 colored textiles also exhibit excellent softness, washability, hydrophilicity, breathability, and tensile properties, making them suitable for practical applications. This work not only provides a practical method for synthesizing noniridescent structural color pigments with high color saturation but also offers new insights into the design of colored passive radiative cooling textiles.

Brilliant non-iridescent structural colors of hierarchical photonic films by hydrophobic substrates assembly design

Hierarchical structure designs can maximize the application of structural materials on multi-dimensional scale from a limited choice. Mimicking this performance is a great challenge, especially in optical structures. Here, a hierarchical structural-colored film with highly ordered periodic layers and amorphous array layers was designed by a simple one-step confined self-assembly procedure based on hydrophobic substrates, which shows an excellent optical effect. The highly ordered periodic layers could act as a specific wavelength mirror-like reflectance, which enhanced the coherent scattering of light in the amorphous arrays, resulting in higher color visibility. The intricate interaction of light over hierarchical structures at different length scales has profound significance for the application of complex optical assemblies.

Non-iridescent structural color patterns with robust mechanical properties produced by two-step photopolymerization

Structural color films with high brightness, saturation and robust mechanical properties have been prepared by a two-step photopolymerization method using colloidal inks. The color saturation of the films could be controlled by the mass of the carbon black (CB) particles and polymerization time while the colors are closely related to the diameter of the CB@SiO2 microspheres. The inks were prepared by dispersing CB@SiO2 microspheres with black CB particles as the core and inorganic SiO2 as the shell in poly(ethylene glycol diacrylate) (PEGDA) resins. The results of bending and rubbing tests showed that the addition of PEGDA prevented the formation of film cracks and enhanced mechanical properties without altering the original color. Structurally colored films were directly attached to a variety of substrates, including glass, metal, paper, and fabric. These colloidal inks have potential application in the fields of displays, paints, and other color-related fields.

Bio-inspired structural colors prepared by using hollow mesoporous silica spheres and carbon black

Solid silica or polystyrene spheres have been widely used to mimic solid melanin for fabricating amorphous photonic structures (APSs) and non-iridescent structural colors. However, few studies have been reported about mimicking APSs from hollow melanosomes in biology. A combination of HMSSs and carbon black (CB) is put forward to mimic hollow melanosomes for obtaining APSs and non-iridescent structural colors. Varied structural colors and reflection peaks of APSs are fabricated by adjusting diameters of HMSSs, amounts of CB and mixing ratios of different HMSSs. The stopband shift (137 nm) of the HMSS APSs infiltrated in ethanol is larger than the 40 nm red shift of solid silica photonic crystals (PCs) and the 105 nm red shift of HMSS PCs. The APSs from HMSSs show high sensitivity in visual detection for the chemicals with similar refractive indices, such as homologues and isomers. Based on structural difference of solid silica spheres and HMSSs, the combined APSs-LR could be obtained from the left side of solid silica spheres and the right side of HMSSs, the APSs-LU are from the lower layer of solid silica spheres and the upper layer of HMSSs. They could be used for information encryption and anti-counterfeiting by adjusting combination ways and the effective refractive indexes. The APSs show great potential applications in display, visual detection, information encryption and anti-counterfeiting.

Construction of cellulose structural-color pigments with tunable colors and iridescence/non-iridescence

Structural colorations have been recognized as a significant way to replace conventional organic dyes for paints, inks, packaging, and cosmetics because of brilliant colors, high stability, and eco-friendliness. However, most current structural-color pigments present an iridescent appearance, and it remains difficult to mitigate a trade-off between lowering the iridescence effect and maintaining the color saturation and brightness. Here, we demonstrate a universal yet economical approach to prepare cellulose structural-color pigments with different sizes. A combined ultrasonication and grinding treatment is explored to adjust the pigment colors as well as control the iridescence-to-non-iridescence transition that depends on the pigment size. The cellulose pigments can be applied on irregular and curved surfaces, having high water-, chemical-, and mechanical-resistances. With humidity-sensing behaviors, the pigments can be further integrated into monitoring systems for environmental management. Such a preparation strategy overcomes the limitation of controlling iridescent and non-iridescent structural colors without sacrificing color properties, which may bring more opportunities to develop new eco-friendly pigments for wide applications.

Construction of Cu2O single crystal nanospheres coating with brilliant structural color and excellent antibacterial properties

Structural coloration as a novel eco-friendly coloring method without using chemical dyes or pigments has been extensively studied for textile coloring. However, structural colors in creatures not only endow them with vivid colors, but also give them special functions. Therefore, the development of functional structural colored textiles with brilliant colors and special functions will have more practical application values. In this study, the structural colored and functional textiles were prepared by one-step spray coating cuprous oxide (Cu2O) single crystal nanospheres on polyethylene terephthalate (PET) fabric. Cu2O single crystal nanospheres with five different diameters were prepared to obtain purple, blue, green, yellow-green and orange noniridescent structural colors due to the Mie scattering of Cu2O nanospheres. Cu2O structural colored fabric showed excellent washing, rubbing and bending colorfastness due to the strong adhesion of polyacrylate (PA). Cu2O structural colored fabric showed excellent antibacterial properties for both Gram-positive and Gram-negative bacteria. The antibacterial rates of Cu2O structural colored fabric after treatment with 60 min for E. coli and S. aureus were close to 100%. Therefore, this research provides the experimental basis for the development of functional structural colored fabrics with brilliant color and excellent antibacterial properties.

Interfacial Colloidal Self-Assembly for Functional Materials

ConspectusSelf-assembly bridges nanoscale and microscale colloidal particles into macroscale functional materials. In particular, self-assembly processes occurring at the liquid/liquid or solid/liquid/air interfaces hold great promise in constructing large-scale two- or three-dimensional (2D or 3D) architectures. Interaction of colloidal particles in the assemblies leads to emergent collective properties not found in individual building blocks, offering a much larger parameter space to tune the material properties. Interfacial self-assembly methods are rapid, cost-effective, scalable, and compatible with existing fabrication technologies, thus promoting widespread interest in a broad range of research fields.Surface chemistry of nanoparticles plays a predominant role in driving the self-assembly of nanoparticles at water/oil interfaces. Amphiphilic nanoparticles coated with mixed polymer brushes or mussel-inspired polydopamine were demonstrated to self-assemble into closely packed thin films, enabling diverse applications from electrochemical sensors and catalysis to surface-enhanced optical properties. Interfacial assemblies of amphiphilic gold nanoparticles were integrated with graphene paper to obtain flexible electrodes in a modular approach. The robust, biocompatible electrodes with exceptional electrocatalytic activities showed excellent sensitivity and reproducibility in biosensing. Recyclable catalysts were prepared by transferring monolayer assemblies of polydopamine-coated nanocatalysts to both hydrophilic and hydrophobic substrates. The immobilized catalysts were easily recovered and recycled without loss of catalytic activity. Plasmonic nanoparticles were self-assembled into a plasmonic substrate for surface-enhanced Raman scattering, metal-enhanced fluorescence, and modulated fluorescence resonance energy transfer (FRET). Strong Raman enhancement was accomplished by rationally directing the Raman probes to the electromagnetic hotspots. Optimal enhancement of fluorescence and FRET was realized by precisely controlling the spacing between the metal surface and the fluorophores and tuning the surface plasmon resonance wavelength of the self-assembled substrate to match the optical properties of the fluorescent dye.At liquid/solid interfaces, infiltration-assisted (IFAST) colloidal self-assembly introduces liquid infiltration in the substrate as a new factor to control the degree of order of the colloidal assemblies. The strong infiltration flow leads to the formation of amorphous colloidal arrays that display noniridescent structural colors. This method is compatible with a broad range of colloidal particle inks, and any solid substrate that is permeable to dispersing liquids but particle-excluding is suitable for IFAST colloidal assembly. Therefore, the IFAST technology offers rapid, scalable fabrication of structural color patterns of diverse colloidal particles with full-spectrum coverage and unprecedented flexibility. Metal-organic framework particles with either spherical or polyhedral morphology were used as ink particles in the Mayer rod coating on wettability patterned photopapers, leading to amorphous photonic structures with vapor-responsive colors. Anticounterfeiting labels have also been developed based on the complex optical features encoded in the photonic structures.Interfacial colloidal self-assembly at the water/oil interface and IFAST assembly at the solid/liquid/air interface have proven to be versatile fabrication platforms to produce functional materials with well-defined properties for diverse applications. These platform technologies are promising in the manufacturing of value-added functional materials.

3D printing of non-iridescent structural color inks for optical anti-counterfeiting.

In this work, structural color inks with practical significance in anti-counterfeiting applications have been successfully manufactured by facilely mixing SiO2@PDA@PHEMA hybrid colloidal particles with the mediated molecules of HEMA. The appropriate rheological properties of these photonic inks provide high viscosity and self-supporting performance, ensuring sufficient interaction between particles to form short-range ordered arrays during the mixing and shearing process and thus generating non-iridescent colors. The strong and broad uniform light absorption capabilities of polydopamine (PDA) not only suppress the incoherent multiple scattering of the photonic inks, but also impart surprising optical anti-counterfeiting properties, i.e. black color under ambient illumination and dazzling reflective coloration under strong illumination. With the 3D printing technique, complicated angle-independent patterns with visualization and high fidelity are expected to be fabricated with the as-prepared photonic inks for real-life applications in smart anti-counterfeiting labels, thus encoding encrypted information and selective color rendering accessories.

Evaluation and Design of Colored Silicon Nanoparticle Systems Using a Bidirectional Deep Neural Network.

Silicon nanoparticles (SiNPs) with lowest-order Mie resonance produce non-iridescent and non-fading vivid structural colors in the visible range. However, the strong wavelength dependence of the radiation pattern and dielectric function makes it very difficult to design nanoparticle systems with the desired colors. Most existing studies focus on monodisperse nanoparticle systems, which are unsuitable for practical applications. This study combined the Lorentz–Mie theory, Monte Carlo, and deep neural networks to evaluate and design colored SiNP systems. The effects of the host medium and particle size distribution on the optical and color properties of the SiNP systems were investigated. A bidirectional deep neural network achieved accurate prediction and inverse design of structural colors. The results demonstrated that the particle size distribution flattened the Mie resonance peak and influenced the reflectance and brightness of the SiNP system. The SiNPs generated vivid colors in all three of the host media. Meanwhile, our proposed neural network model achieved a near-perfect prediction of colors with high accuracy of the designed geometric parameters. This work accurately and efficiently evaluates and designs the optical and color properties of SiNP systems, thus accelerating the design process and contributing to the practical production design of color inks, decoration, and printing.

The Development of New Catalytic Pigments Based on SiO2 Amorphous Photonic Crystals via Adding of Dual-Functional Black TiO2-x Nanoparticles.

Biomimetic synthesis of amorphous photonic crystals (APCs) is an effective approach to obtaining non-iridescent structural colors. However, the structural colors of artificially prepared APCs are dim or even white due to the influence of incoherent scattering. In this paper, we present a novel method to combine APCs with black TiO2-x to construct a noniridescent structural color pigments with high visibility and photocatalytic activity. Due to the absorption of incoherently scattered light by black TiO2-x, the color saturation of structural colors has been significantly increased. In addition, the utilization rate of photogenic carriers was effectively enhanced by the slow light effect generated from the pseudoband gap of SiO2 APCs with TiO2-x absorbed full spectrum. The tone and color saturation of catalytic pigments is controlled by the diameter of SiO2 nanospheres and the ratio of TiO2-x nanoparticles, which provides a controllable application study in color-related fields as artwork, environmental coatings, and textiles.

Rapid Assembly of Magnetoplasmonic Photonic Arrays for Brilliant, Noniridescent, and Stimuli-Responsive Structural Colors.

There are usually trade-offs between maximizing the color saturation and brightness and minimizing the angle-dependent effect in structural colors. Here, a magnetic field-induced assembly for the rapid formation of scalable, uniform amorphous photonic arrays (APAs) featuring unique structural colors is demonstrated. The magnetic field plays a fundamental role in photonic film formation, making this assembly technology versatile for developing structural color patterns on arbitrary substrates. The synergistic combination of surface plasmonic resonance of the Ag core and broadband light absorption of high refractive index (RI) Fe3 O4 shell in hybrid magnetoplasmonic nanoparticles (MagPlas NPs) enables breaking the trade-offs to produce brilliant, noniridescent structural colors with high tunability and responsiveness. These features enable the fabrication of various types of highly sensitive and reliable colorimetric sensors for naked-eye detection without sophisticated instruments. Furthermore, large-scale structural color patterns are effortlessly achieved, demonstrating the high potential of the present approach for full-spectrum displays, active coatings, and rewritable papers.

Structural Color Spectral Response of Dense Structures of Discoidal Particles Generated by Evaporative Assembly.

Structural color─optical response due to light diffraction or scattering from submicrometer-scale structures─is a promising means for sustainable coloration. To expand the functionality of structural color, we introduce discoidal shape anisotropy into colloidal particles and characterize how structural color reflection can be engineered. Uniaxial compression of spheres is used to prepare discoids with varying shape anisotropy and particle size. Discoids are assembled into thin films by evaporation. We find that structural color of assembled films displays components due to diffuse backscattering and multilayer reflection. As discoids become more anisotropic, the assembled structure is more disordered. The multilayer reflection is suppressed─peak height becomes smaller and peak width broader; thus, the color is predominantly from diffuse backscattering. Finally, the discoid structural color can be tuned by varying particle size and has low dependence on viewing angle. We corroborate our results by comparing experimental microstructures and measured reflection spectra with Monte Carlo simulations and calculated spectra by finite-difference time-domain simulation. Our findings demonstrate that the two tunable geometries of discoids─size and aspect ratio─generate different effects on spectral response and therefore can function as independent design parameters that expand possibilities for producing noniridescent structural color.