Examples: Improve background color of WebGPU demo.

examples/webgpu_sandbox.html

@@ -28,7 +28,7 @@
 				camera.position.z = 4;
 
 				scene = new THREE.Scene();
-				scene.background = new THREE.Color( 0xffffff );
+				scene.background = new THREE.Color( 0x222222 );
 
 				// textured mesh