I change the colors out on my Prusa XL pretty often - this leads to my terrible memory forgetting what color I have loaded much less if I swapped it for PETG vs PLA.

There were some other models for this but nothing that fit what I wanted - a quick way to see the color and type loaded.  

I use Prusaslicer to add the letters, usually in a contrasting color.     I've included  PETG & PLA chips ready to print and the blender files as well.