At setAdditionalColor(). Nothing wrong with a mention. It's just the docs. By the way, the ShadowHelper doesn't seem to consider object opacity. The following two lines produce a completely opaque shadow.
eyeLaser1 = new Polyline(points, new java.awt.Color(255, 0, 0, 155));
eyeLaser1.setTransparencyMode(Object3D.TRANSPARENCY_MODE_ADD);