Python script that computes the Kubelka–Munk diffuse reflectance of (i) bare 20-nm TiN or HfN nanoparticles and (ii) MN/SiO2 core–shell composite particles (20-nm core, 50-nm SiO2 shell, 120-nm outer diameter), using quasi-static (Rayleigh) Mie cross sections and a Drude–Lorentz dielectric function in which only the plasma frequency ωp is calibrated to the experimental dispersion-phase LSPR via the Fröhlich condition. The script reproduces Figure 10 of: S. Noguchi, T. Fang, Y. Fujii and K. Tadanaga, "Silica encapsulation of TiN and HfN nanoparticles by sol–gel processing: preserving plasmonic coloration of metal-nitride powders in the solid state", manuscript submitted for publication (2026). It implements the procedure described in Section S3 of the Supplementary Information of the article. Dependencies: Python 3, NumPy, SciPy, Matplotlib. See README.md for usage.