Board Thread:General Discussion/@comment-121.217.139.187-20130907025835/@comment-17732608-20130907052623

It is most likely Aura that's affecting the color of Nora's weapon blasts, but it could also just as easily be a 'special blend' of Dust she uses in the shells.

Until the series explains more about the properties of Aura and Dust, this guess is as good as any.