<p>Cellulose nanocrystals (CNCs) self-assemble into cholesteric phase liquid crystals (CPLCs) at a critical concentration in aqueous suspension. The resulting helical structure is retained in the solid-state film, generating left-handed circularly polarized structural color. Optical materials based on CNC CPLCs have attracted extensive interest; however, their assembly is highly sensitive to environmental and interfacial conditions, complicating structural color control. This study investigates the effects of substrate surface properties—surface energy, water absorption, and contact angle—on the self-assembly of CNC photonic thin films. Responsive CNC-based cholesteric films were fabricated by incorporating glucose (Glc) and carbon black (CB) into CNC suspensions and co-assembling the mixture on printing paper via evaporation-induced self-assembly (EISA). The resulting films exhibit a left-handed helical architecture with birefringence and show high humidity response across the ultraviolet (UV) to near-infrared (NIR) range. The CNC/Glc/CB composite films also demonstrate excellent stability and reversibility, offering a promising strategy for applications such as humidity sensing and information encryption.</p> Graphical Abstract <p></p>