Printed face down with 3 colours, black, white and blue which are mixed within this first 3 layers to create different shades.
I used flexible magnetic paper on the back to turn it into a magnet, you could also glue magnets on.
Printing smaller may work with a 0.2mm nozzle but the lines are about as thin as a 0.4mm nozzle can print, printing it bigger should be possible but do not increase or decrease the z axis