Examples: force background color on ascii example

examples/webgl_effects_ascii.html

@@ -33,6 +33,7 @@
 				camera.position.z = 500;
 
 				scene = new THREE.Scene();
+				scene.background = new THREE.Color( 0, 0, 0 );
 
 				var light = new THREE.PointLight( 0xffffff );
 				light.position.set( 500, 500, 500 );