Red Team Block

The Traveling Merchant is the only supplier, and he brings one color per visit along with the platform that matches it. There is no recipe and no other source, so a full set means catching him on six separate days with the right stock. Buy deep when a color you want appears, because you have no idea when it comes around again.

Despite the name they have nothing to do with teams. They do not recolor to match yours or react to who walks on them, unlike Team Dye. What you get is a clean block in a strong flat color, which Terraria is short on. Builders use them for signage, floor markers, and color blocking, and on a PvP map they mark which half of the arena belongs to whom. The dull variants that come out of Shimmer are the same colors turned down, which reads better across a large surface.

An unused line of text in the game files talks about not being able to switch teams while standing inside your own team's blocks. It was never wired up, so the blocks really are inert, but it suggests they were once meant to do something in multiplayer.