Quick Answer

In Welcome to Bloxburg (Roblox), the “rainbow square” most players talk about is the Mysterious Cube Trophy —a build-mode item that looks like a semi‑transparent cube in the inventory but appears as a rainbow‑colored cube when placed.

What the Rainbow Square Actually Is

Mysterious Cube Trophy

  • Inventory appearance: semi‑transparent cube icon in Build Mode.
  • Placed appearance: a tilted, rainbow cube that cycles colors, giving it that “rainbow square” look.
  • Category: decorative trophy / collectible item in the game’s build catalog.

Players often call it “rainbow square” or “rainbow cube” because of how it looks once it’s placed on a plot.

How It’s Used

Common uses in builds:

  • Decor piece in modern or colorful houses
  • Accent on shelves, desks, or display areas
  • Part of rainbow‑themed rooms or “pride” builds (some creators explicitly use rainbow items for this).

Why People Ask About It

You’ll see questions like “what is the rainbow square in bloxburg” mostly because:

  • The item’s name (Mysterious Cube Trophy) doesn’t obviously say “rainbow,” so new players recognize it by its look.
  • It stands out visually, so people notice it in other players’ houses and want to know how to get it.

How to Find / Place It (General Idea)

While exact catalog location can change with updates, the typical process is:

  1. Open Build Mode.
  2. Go to the Trophies / Decorations section (or search “cube” / “mysterious” if your UI has search).
  3. Look for the Mysterious Cube Trophy with the semi‑transparent cube icon.
  1. Place it on your plot; it will show as the rainbow cube.

Costs follow normal painting/material rules if you modify it: changing color is $5 per side, material is $20 per side using the Paint Tool.

TL;DR

  • The “rainbow square” in Bloxburg = Mysterious Cube Trophy.
  • It looks like a plain cube in the menu but becomes a rainbow‑colored cube when placed.
  • It’s a decorative item used for colorful builds and displays.

Information gathered from public forums or data available on the internet and portrayed here.