Holance
Holance
You need to adjust your material properties. And you don't need so many directional lights. Usually one is enough, just bind the direction light direction to camera view direction.
You can assign a color gradient texture to the material and assigned texture coordinates on different vertices to sample the texture.
How do you remove the object? You can try to call Viewport3DX. InvalidateSceneGraph function, but it should be called automatically when node is removed.