Rainbow Brick

Rainbow Brick is a Hardmode brick that can be obtained as a drop from the Rainbow Slime. They cycle through the colors of the rainbow. The cycling colors of Rainbow Brick Walls, Rainbow Torches, the Disco Ball and Rainbow Hair Dye are synchronized with each other. When a waterfall passes over a Rainbow Brick, hammered once, the water will also cycle through the colors.

Trivia

 * Next to Lihzahrd Brick, Rainbow Bricks are one of the hardest blocks to obtain, because under usual circumstances, the only way to obtain them is to defeat Rainbow Slimes, some of the rarest enemies in the entire game. Despite this, Rainbow Bricks still only have a rarity of blue (third lowest, behind gray and white).
 * However, in worlds, Underground Cabins are occasionally made of Rainbow Bricks, which makes them easier to collect.
 * The aesthetic of the brick, when placed, will either have the rectangular appearance of a standard brick, such as a Gray Brick, or a uniform blank appearance, such as that of a Smooth Marble Block. It may also change between one and the other when hammered. This can make it a rather tedious building material to use.
 * Rainbow Bricks will still maintain their rainbow-glowing effect even when painted.