Just set a pause print at the top of the magnet and two filament changes.
White then blue then red.
I found that slowing the print speed after changing filament helped with the narrow lines.
Designed for 0.2mm layers.
I used a 10x2.5mm magnet and one model has a hole sized for that. I also included a solid model so you can add a void for whatever magnet you have on hand.
Also please check out my Buffalo Bills magnet.
https://www.printables.com/model/511151-buffalo-bills-magnet
The author marked this model as their own original creation.