Confetti Block

The crafting station it wants puts it behind Hardmode, which is an odd gate for a party decoration but does mean most people meet it long after they stopped needing new block types.

Placed, it is see-through with confetti drifting behind it, so it works as a window in a celebration room or as a layer where you want movement without hiding what is on the other side. If the transparency ruins the effect in a dark build, the midnight variant keeps the falling confetti and drops the glass.