Teal Mushroom

Do not swing at it. Unlike almost every other plant in the game, hitting this with a weapon destroys it and leaves you nothing. It only comes up under a pickaxe. That single rule is why people walk past hundreds of them across a playthrough without ever picking one.

It is a dye plant and nothing more, so color is the only reason to gather any. Spelunker highlights it the way it highlights ore, which turns a potion you were probably already drinking into a fast way to spot them across a dark cavern.

It is not fussy about grass the way most mushrooms are and will come up on plain dirt, stone or mud below the surface. The exception is the converted stone types: corrupt, crimson and hallowed ground will not grow it, so a world that an evil biome has chewed through gets steadily worse to farm.