Blue zodiac costume was removed from RuneScape after an update, but still exists in-game for those who had obtained it.
A blue zodiac costume is an item involved with the Zodiac TrainingTreasure Hunter promotion. It is gained from prestiging the zodiac card two times. The player can choose to appear as the head, middle or tail of the outfit to use in conjunction with other players. Like the other zodiac costumes, the player is unable to attack while wearing this costume. This item cannot be keepsaked.