title: Threejs: assign different colors to each vertex in a geometry
body: <p>I want to do picking via IdMapping in Three.js</p>
  
  <p>Because of performance issues I only have one huge geometry, computed like this:</p>
  
  <pre><code>for (var i = 0; i &lt; numberOfVertices; i += 9) {
    p1  = new THREE.Vector3(graphData.triangles.vertices[i+0], graphData.triangles.vertices[i+1], graphData.triangles.vertices[i+2]);
    p2  = new THREE.Vector3(graphData.triangles.vertices[i+3], graphData.triangles.vertices[i+4], graphData.triangles.vertices[i+5]);
    p3  = new THREE.Vector3(graphData.triangles.vertices[i+6], graphData.triangles.vertices[i+7], graphData.triangles.vertices[i+8]);
    geometry.vertices.push(new THREE.Vertex( p1.clone() ));
    geometry.vertices.push(new THREE.Vertex( p2.clone() ));
    geometry.vertices.push(new THREE.Vertex( p3.clone() ));
    geometry.faces.push( new THREE.Face3( i/3, i/3+1, i/3+2 ) );
  
    // i want to do something like this:
    geometry.colors.push(new THREE.Color(0xFF0000));
    geometry.colors.push(new THREE.Color(0xFF0000));
    geometry.colors.push(new THREE.Color(0xFF0000)); 
  }
  
  geometry.computeFaceNormals();
  var material = new THREE.MeshBasicMaterial({});
  
  var triangles = new THREE.Mesh( geometry, material );
  scene.add(triangles);
  </code></pre>
  
  <p>How can I assign different colors to each vertex in my geometry?</p>