three.jsによる透明な背景

コードは機能しますが、three.jsを使用してキャンバスに透明な背景を設定する際に問題が発生します。私が使う：

Background.renderer.setClearColor(0xffffff, 0);

しかし、その後、背景が黒くなります。どうすれば透明に変更できますか？

コード：

   var camera, scene, renderer;
   var mouseX = 0, mouseY = 0;
   var p;

   var windowHalfX = site.Width / 2;
   var windowHalfY = site.Height / 2;

   Background.camera = new THREE.PerspectiveCamera( 35, site.Width / site.Height, 1, 2000 );
   Background.camera.position.z = 300;
   //camera.position.y = 200;

   // scene
   Background.scene = new THREE.Scene();

   // texture
   var manager = new THREE.LoadingManager();
   manager.onProgress = function ( item, loaded, total ) {
      console.log('webgl, twice??');
      //console.log( item, loaded, total );
   };


   // particles
   var p_geom = new THREE.Geometry();
   var p_material = new THREE.ParticleBasicMaterial({
      color: 0xFFFFFF,
      size: 1
   });

   // model
   var loader = new THREE.OBJLoader( manager );
   loader.load( site.base_url + '/assets/models/head.obj', function ( object ) {

      object.traverse( function ( child ) {

         if ( child instanceof THREE.Mesh ) {

            // child.material.map = texture;

            var scale = 6;

            $(child.geometry.vertices).each(function() {
               p_geom.vertices.push(new THREE.Vector3(this.x * scale, this.y * scale, this.z * scale));
            })
         }
      });

      Background.scene.add(p)
   });

   p = new THREE.ParticleSystem(
      p_geom,
      p_material
   );

   Background.renderer = new THREE.WebGLRenderer();
   Background.renderer.setSize( site.Width, site.Height );
   Background.renderer.setClearColor(0xffffff, 0);

   $('.particlehead').append(Background.renderer.domElement);
   $('#content').on('mousemove', onDocumentMouseMove);
   site.window.on('resize', onWindowResize);

   function onWindowResize() {
      windowHalfX = site.Width / 2;
      windowHalfY = site.Height / 2;
      //console.log(windowHalfX);

      Background.camera.aspect = site.Width / site.Height;
      Background.camera.updateProjectionMatrix();

      Background.renderer.setSize( site.Width, site.Height );
   }

   function onDocumentMouseMove( event ) {
      mouseX = ( event.clientX - windowHalfX ) / 2;
      mouseY = ( event.clientY - windowHalfY ) / 2;
      //console.log(mouseX)
   }

   Background.animate = function() { 

      //console.log('animate2');
      Background.ticker = TweenMax.ticker;
      Background.ticker.addEventListener("tick", Background.animate);

      render();
   }

   function render() {
      Background.camera.position.x += ( (mouseX * .5) - Background.camera.position.x ) * .05;
      Background.camera.position.y += ( -(mouseY * .5) - Background.camera.position.y ) * .05;

      Background.camera.lookAt( Background.scene.position );

      Background.renderer.render( Background.scene, Background.camera );
   }

   render();

three.jsで透明な背景が必要な場合alphaは、WebGLRendererコンストラクターにパラメーターを渡す必要があります。

var renderer = new THREE.WebGLRenderer( { alpha: true } );

クリアカラーはデフォルト値のままにしておくことができます。

renderer.setClearColor( 0x000000, 0 ); // the default

three.js r.71