Rainbow Brick

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

Trivia

 * Next to Lihzahrd Brick, Rainbow Bricks are one of the hardest blocks to obtain, being that they never occur in the environment, cannot be crafted, and only drop from Rainbow Slimes. Despite this, Rainbow Bricks still only have a rarity of white (second lowest only behind gray which only applies to trash items and white tier tools with negative modifiers).
 * If you let water pass through rainbow brick by turning the brick into a slab, it will cause the water to change color with it.
 * 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.

History
Brique arc-en-ciel