Don't clear anything.
This will leave colors and depth buffer from the previous frame or whatever was displayed before. See Also: Camera.clearFlags property, camera component.
// Don't clear anything camera.clearFlags = CameraClearFlags.Nothing;
using UnityEngine; using System.Collections; public class ExampleClass : MonoBehaviour { void Example() { camera.clearFlags = CameraClearFlags.Nothing; } }
import UnityEngine import System.Collections public class ExampleClass(MonoBehaviour): def Example() as void: camera.clearFlags = CameraClearFlags.Nothing