Function pick_material_style_for_submesh 

pub fn pick_material_style_for_submesh(
    colors: &[[f32; 4]],
    prefer_transparent: bool,
) -> Option<[f32; 4]>

Pick a material colour for one sub-mesh, alternating preference so a window distributes its frame (opaque) and glazing (transparent) colours across sub-meshes instead of painting every part the same. prefer_transparent is toggled by the caller per sub-mesh.