The widespread use of spot color inks in packaging printing has led to the accumulation of substantial remaining spot color inks, resulting in resource waste and environmental concerns. This study proposes a novel utilization method for remaining spot color inks that integrates Delaunay triangulation with the single-constant Kubelka–Munk (K–M) theory to achieve precise and efficient reuse. A color matching database was first established based on the spectral reflectance and colorimetric properties of base and remaining spot color inks. The Delaunay triangulation algorithm was applied in the CIE L^∗a^∗b^∗ space to construct a 3D color gamut structure, enabling the identification of feasible ink combinations through tetrahedral inclusion analysis. Subsequently, an inverse color matching model based on the single-constant K–M theory was developed to optimize ink formulations for given target colors. Experimental validation using multiple remaining spot color targets demonstrated that the predicted and practical color differences (ΔE) remained below 3. This approach not only improves the reuse rate of the remaining spot color inks but also offers a systematic and scalable solution for resource-efficient color management in industrial printing.