Abyssal blue dye is an item that allows one piece of the raiments of the eye to be recoloured to a blue variant. It is a one time use per item, therefore a total of three are needed to recolour a full set, with optionally two more for the amulet of the eye and the lost bag.
Excess blue dyes can be exchanged for an abyssal red or abyssal green dye by using it on Apprentice Felix; however, doing so does not count towards unlocking the respective slots in the collection log. Players may also choose to exchange the dye with Apprentice Felix for 50 abyssal pearls instead.