Information
Sometimes, especially in older meshes used by X-Morph, the material is baked directly into the mesh file. How to solve this problem when trying to use a different material is listed here.
Find the baked material name
Open the *.mesh file with a desired Hex-Editor or even Notepad, and search for a fitting name, example:
Which shows “projectiles/railgun_projectile_beam” as text.
Override used material
You can override used material by just adding a “material” field to MeshDesc of the entity file: