You should be able to accomplish this by setting the following properties:
- On the scene, set the base surface opacity to 0 to prevent rendering the ground: sceneView.Scene.BaseSurface.Opacity = 0;
- On the scene view, set the atmosphere effect to none - this will prevent rendering of the blue/gray sky: myScene.BaseSurface.Opacity = 0;
- If you're not interested in showing the attribution bar, you can disable that with sceneView.IsAttributionTextVisible. (note: be sure to follow the terms listed: https://developers.arcgis.com/terms/attribution/)
In a future release, Runtime will support specifying options for the space effect (black background with stars). With that change, you'll be able to disable rendering the background so that the view behind the scene view is visible. That should enable you to display a model directly on top of your views without anything else visible.
