Try something like Config.nearPlane+0.xf instead of 0. 0 makes no sense and will be silently adjusted to Config.nearPlane+1. However, you may still run into this kind of problem, because an Overlay is actually an Object3D and as such, it interacts with the rest of the scene. If you don't want this, you have two options: Use blitting instead or put all Overlays into a separate World-instance, which will be rendered after the main world. Remember to clear the zbuffer between the renderings.