Change diffuse color to a material

How can I customize the diffuse color for the default material? This is my code:

fn initialize(world: &mut World) {
        let mesh = world.exec(|loader: AssetLoaderSystemData<'_, Mesh>| {
            loader.load_from_data(
                Shape::Cube
                    .generate::<(Vec<Position>, Vec<Normal>, Vec<Tangent>, Vec<TexCoord>)>(None)
                    .into(),
                (),
            )
        });

        let material_defaults = world.read_resource::<MaterialDefaults>().0.clone();
        let material = world.exec(|loader: AssetLoaderSystemData<'_, Material>| {
            loader.load_from_data(
                Material {
                    ..material_defaults
                },
                (),
            )
        });

        world
            .create_entity()
            .with(mesh)
            .with(material)
            .build();
}