This study developed a high-performance colorimetric humidity sensor by depositing platinum (Pt) nanoparticles onto a silver (Ag)-based thin metal film through a sputtering process, aimed at enhancing plasmonic resonance effects. The incorporation of Pt nanoparticles addressed limitations in conventional Ag-based structures by significantly improving the sensor\'s sensitivity to humidity changes and accelerating its response time. UV-Vis reflectance spectrum analysis revealed that Pt coating effectively induced plasmonic resonance, leading to noticeable reflectance changes under varying humidity conditions. Additionally, structural analyses using SEM, AFM, and XRD confirmed that Pt deposition preserved the physical and crystallographic stability of the Ag-based structure while maintaining its surface uniformity. The sensor exhibited rapid responsiveness, with almost immediate detection of humidity changes and a full recovery to its original state within a second. These results highlight the sensor\'s potential as an innovative solution for real-time air pollution monitoring, environmental control systems, and other humidity-sensitive applications.