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High-quality and brilliant structural colors have been successfully produced using solution-based process over the past decade. 

Abstract Iridescent color-shift pigments have been used in some industrial applications, e.g., for cosmetics and packaging. To achieve environmental-friendly and lasting color, thin-film interference is used to generate structural color. By maximizing the refractive index (RI) difference between the thin films (i.e., using an ultralow RI film), super-iridescent structural color can be produced. While the lowest refractive index of a naturally occurring solid dielectric is close to 1.37 (i.e., MgF₂), we synthesized highly porous dielectric SiO₂aerogel to achieve ultralow-RI (n ~ 1.06) and demonstrated a high-refractive index/low-refractive index/absorber (HLA) trilayer structural color. The achieved structural color is highly iridescent and capable of tracing a near-closed loop in CIE color space. By tuning the refractive index, thickness, and geometry of the aerogel layer, we control the reflection dip’s shape, therefore producing a wide range of vivid and iridescent colors.