A simple ring specifically designed for multimaterial printing. Can be printed in all one color, or you can easily recolor the stripe in the middle using the Bambu Studio color fill tool.
The ring can be easily resized in the slicer. At 100%, it's roughly size 7 ¾. I scaled it to 105% to fit my finger, which makes it just below size 9. I'd recommend printing a test print in a single color to size it to your finger before printing the final model.