In 2015 I created some 3D printed Christmas ornaments as seen here. It occurred to me the other day that the tree ornament was just about the right size to sit on top of an Adafruit Circuit Playground Express. The Neopixels would reflect upward onto the ornament. I would have to resize it slightly and cut out some notches for the USB port and JST power connector.
I printed it using white PLA and I think it turned out pretty well. I also have some transparent T-Glaze filament that I may try as well. Here are some photos and a YouTube video showing how it looks.