In this study, we present a color scale-based approach for the rapid and sensitive visual detection of lead(II) in human urine using a polymer-based optical sensor. The optimized optode membrane demonstrates a detection limit of 6 ± 4 μg × L−1, making it suitable for both point-of-care diagnostics and environmental applications. Response characteristics, including median signal, dynamic range, and response time, were evaluated, and the influence of membrane composition, both qualitative and quantitative, on optical performance was systematically investigated. A color scale was developed for semi-quantitative, camera-based express analysis and validated using urine samples. The results obtained with this method showed good agreement with conventional techniques such as potentiometry and spectrophotometry. This confirms the feasibility of combining the colorimetric sensor with a printed scale for rapid, equipment-free lead(II) detection. To support field deployment, we designed a disposable test device that integrates the optode membrane with a sample container, enabling rapid, equipment-free classification of lead(II) levels. This approach offers a cost-effective alternative to traditional methods, enabling point-of-care screening and in situ environmental monitoring of lead contamination in at-risk populations.