Summary

I couldn't find anything like this on thingiverse yet, so I quickly made these up in freecad.
These fit over small filing cabinet or desk keys, so you can tell them apart. They might not fit your keys if the shape or holes are different.

I had to scale them to 115% X axis to get them to fit over the key properly, some filing was also required to get the keys to fit.

All printed in PLA, all but the silver one in the pictures are 0.1mm Layers, with a 0.5mmx0.5mm starting layer. If you have the first layer width 1mm slic3r won't print this well.
The Silver one in the picture is a 0.5mm layer height because it was a prototype.