Abstract Objectives This study aimed to qualitatively and quantitatively assess the masking efficacy and color stability of resin infiltration on post-orthodontic ICL after 1 year. Materials and methods In 17 adolescents, 112 ICL (ICDAS-1: n = 1; ICDAS-2: n = 111) in 112 teeth were treated by resin infiltration (Icon, DMG) 3 to 12 months after bracket removal. The etching procedure was performed up to 3 times. Standardized digital images were taken before treatment (T₀), 7 days (T₇) and 12 months (T₃₆₅) after treatment. Outcomes included the evaluation of the color differences between infiltrated and healthy enamel at T₀, T₇, and T₃₆₅ by quantitative (colorimetric analysis (ΔE), ICDAS scores) and qualitative methods (5-point Likert scale (deteriorated (1), unchanged (2), improved, but not satisfying (3), improved and no further treatment required (4), completely masked (5)).) Differences between time points were analyzed by using Friedman test (ΔΕ) and chi-square tests (ICDAS). Results The median color difference (25^th/75^th percentiles) between carious and healthy enamel at baseline (ΔΕ₀) was 10.2(7.7/13.6). A significant decrease was observed 7 days after treatment (ΔΕ₇ = 3.1(1.8/5.0); p < 0.001; ICDAS; p < 0.001). No significant changes based on ΔΕ (p = 1.000), and ICDAS grade (p = 0.305) were observed between T₇ and T₃₆₅ (ΔΕ₁₂ = 3.4 (1.8/4.9)). Furthermore, at T₃₆₅ four experienced dentists classified 55% and 39% of the lesions as “improved and no further treatment required” and “completely masked,” respectively (Fleiss kappa: T₃₆₅ = 0.851 (almost perfect)). Conclusion Resin infiltration efficaciously masked post-orthodontic ICL 7 days and 12 months after treatment. These results for most of the teeth could not only be observed by quantitative but also by qualitative analysis. Clinical relevance Resin infiltration efficaciously masks post-orthodontic initial carious lesions. The optical improvement can be observed directly after treatment and remains stable for at least 12 months.