I was hoping to create the effect of a cube being lit from the inside. So I applied the following approach:

1. Create a material with some alpha, eg.
  var red : ColorMaterial = new ColorMaterial(0xffffff, .5);

2. Create a light with some color, eg.
  var light : PointLight = new PointLight();
  light.color = 0xff0000;

3. Create a cube using the light
  red.lights = [light];
  var cube : Cube = new Cube(red);
 
4. Add both to scene
  scene.addChild(light);
  scene.addChild(cube);

Now we should have a basic white cube at (0,0,0) and a red light inside it at (0,0,0). When I render the scene I see only a grayish cube. If I move the light ouside of the cube I can see the red color hitting the applicable faces.

What am I doing wrong?

Unfortunately this won’t work, because light is calculated using the normals of a mesh’s geometry, and can’t travel through it. You will likely want to fake this some other way, but also consider trying sub-surface scattering which will simulate translucency.

You can “bend” the normals to point inward (do not change the winding order, though). It is also possible to invert the whole model and then render it with front-face culling.

Best regards.