Oh this is neat! The author is very elusive on the details sadly, but the results look good, and the process probably has room for improvement if you’re willing to edit GCode or do some advanced slicer magic.
Looks like this reddit post has a lot more details:
I’ll definitely experiment with that soon. Posted in another thread, I’ve been exploring the possibility of making translucent faceplates with PETG with decent but not amazing results.