A device for applying a magnetic field to a container comprises an adjustable magnetic field generator. The adjustable magnetic field generator is adjacent to the container and has a magnet having one magnetic pole adjacent a wall of the container and another magnetic pole away from the wall of the container. The adjustable magnetic field generator comprises a magnet. The intensity of magnetic field applied to the container gradually decreases from the container wall adjacent the magnetic pole of the magnet to the opposite container wall. Method for coloring anode coatings using the coloring device is also provided.