Just colored glass.
I've been dealing w/ a place called Alpine glass for many years now, they have an insane assortment of choices of colored and stained glass(And not in Alpine but rather El Cajon)
This is their fb page
https://www.facebook.com/Alpine-Stai...5811359151877/
Most of my tanks were under T5 and LEDs unless they were before LEDs really came on.
It was just an option I added after using glass on my base cabs initially to get something out of my sump lights for an added detail, and eventually I went w/ something to personalize my own tank canopy.
Here's another I did long ago w/ glass just on base, and my pics should link to an album w/ other examples if you click on pic.