A Piano keychain or backpack tag. I could not find any I liked, so I made one using sketchup. You can scale to the size you like.

I did this with a single extruder. Just pause and swap colors. Black to white and back to black. If you print .3mm layers and same size you load black first, then once you start layer at 2.3mm you change to white, and then when you start layer 5.9mm you change back to black.

Good Luck