Blue is a Warforged that the PCs met at the Red Hammer. It was introduced to them by Crucible after it was revealed that the PCs were investigating the recent murders of various Warforged, particularly that of Pater (a friend of Professor Gydd Nepherett).
Blue has also been investigating the recent murders and heavily suspects that the followers of The Lord of Blades are to blame. His reasoning is that all the Warforged that have been murdered so far have been friends of non-Warforged races and they are being killed to make examples to others of the race. He suggested the PCs investigate further at the Jack of Blades, another Warforged bar that caters specifically to followers of The Lord of Blades.