Materials are instantiated and cached at runtime for better performance and because Nature Renderer has to set a few additional settings for your materials. This means that if you make a change to the material then these changes are not shown.
Call NatureRenderer.FlushMaterials to apply and show the changes. This will update the internal materials with the new changes.
Using VisualDesignCafe.Rendering.Nature; GetComponent<NatureRenderer>().FlushMaterials();