User blog comment:Kogath/Monster Hunter X Discussion/@comment-6050823-20151210020343/@comment-4009941-20151210031014

This also explains some of teh features of Frontiers HC Tigrex. It also has the blue claws, blue on it's wings. and blue on it's tail. The roar info is also the same.

Though the blue develpment of "Hook Claws" seems to be much more extreme than HC Tigrex who only appear to just be old male Tigrex who likely grew the blue from age I guess.