Probably not the first, but I found out that light gray stained glass panes are invisible in inventory : r/Minecraft
Light Gray Stained Glass | Minecraft Universe Wiki | Fandom
Apollo DesignScapes Fluorescent Light Cover Insert – Gem Stained Glass - Enhance Mood and Reduce Stress - Made from Lightweight, fire-Retardant Film - Easy to Install - This is NOT The Cover Panel - Amazon.com