title: RealityKit Change USDZ diffuse material at runtime
body: <p>I am loading a USDZ model with RealityKit in Swift. The model loads fine with it's texture.</p>
  
  <p>However, I am unable to change the diffuse property of the material, the material always comes back as <code>AnyMaterial</code>.</p>
  
  <p>I can override the material completely with a <code>SimpleMaterial</code> or I can change the USDZ diffuse colour before running the app, but can't seem to do this at run time, any ideas?</p>
  
  <p>I just want to be able to change the one property</p>
  
  <pre><code>/*
  Find an entity within the parent, and find the material, test to try and change it's material
  **/
  private func updateColor(entity: Entity) {
  
      guard
          let found = entity.findEntity(named: "MyItem"),
          var modelComponent = found.components[ModelComponent] as? ModelComponent,
          let existingMaterial = modelComponent.materials.first else {
          return
      }
  
      // This is `AnyMaterial` - no diffuse property
      // What can I use here to change the diffuse?
      modelComponent.materials = [existingMaterial]
  
      // Change to yellow for testing
      //var material = SimpleMaterial()
      //material.baseColor = .color(.yellow)
      //modelComponent.materials = [material]
  
      found.components.set(modelComponent)
  }
  </code></pre>