Minecraft wiki entry for Glass, associated text: First picture of glass in a test version of 0.0.18a_02.
The first image of stained glass released by Mojang. Behind the glass is a cat and Grum.
The original look of the stained glass blocks.
Stained glass as of 1.14.4
Stained glass changing the beacon's color.
Glass being obtained by trading with a cartographer villager.