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The structural color of photonic crystals is usually whitish and has low saturation due to multiple incoherent scattering effects, limiting its application in practical visual observation. Herein, by controlling the calcination time of PS@SiO 2 nanoparticles, we obtain hollow SiO 2 with different in situ generated carbon black contents and assemble them into photonic crystal inks (PCIs). PCIs have excellent saturation and high crystallinity due to the in-situ generated carbon black capable of absorbing incoherently scattered light without affecting particle assembly. PCIs are further converted into non-close-packed photonic crystal films with highly saturated structural colors by photopolymerization of resins. This photonic crystal film can be swollen by an ethanol-water mixture, resulting in structural color changes and shifts in reflection peaks. Moreover, the photonic crystal film can dynamically change from a dry opaque state to an ethanol-wetted translucent state. Such solvent-responsive photonic crystal films with highly saturated structural colors are expected to be used in alcohol sensors and color anti-counterfeiting labels. We introduce carbon black in situ in h-SiO 2 cores to suppress incoherent scattering and enable them to assemble into photonic crystal inks (PCIs) with high saturation structural colors, and the amount of generated in situ carbon black can easily adjust the saturation of the structural color of PCIs. PCIs are further converted into non-close-packed photonic crystal film with highly saturated structural colors by photopolymerization of resins, and this film can be applied to visually detect ethanol-water mixtures and color security labels. [Display omitted] • A series of high-quality h-SiO 2 with different in situ generated carbon black contents are synthesized. • C@h-SiO 2 can be assembled into PCIs through electrostatic repulsion and solvation forces. • PCIs have excellent saturation and high crystallinity. • PCIs can transform into non-close-packed photonic crystal films for solvent detection and anti-counterfeiting labels. [ABSTRACT FROM AUTHOR]