Pink goblin mail is made by using pink dye (bought from Betty in Port Sarim) on goblin mail. Like all goblin mail, it is too small for players to normally wear as armour.
However, during the Land of the Goblins quest the player can turn into a goblin using a transmogrification potion to access the tribal areas of the Goblin Cave and can then wear the pink goblin mail, though there is no tribe that wears pink goblin mail.
Pink goblin mail cannot be traded, but can still have value. It can occupy space in the inventory or bank. However, the brown goblin mail is tradeable and the dye is easy to obtain if you have completed The Hand in the Sand quest.