User blog comment:ChishioKunrin/Dust: Fire! Water! Lightning! Energy?/@comment-24435688-20140822042944

Well, we saw Glynda using some purple energy in the first episode, so I don't think that it's exclusive to Weiss, but it definitely seems to be one the rarer types of Dust.

Assuming of course that Glynda was using Dust during that fight and it wasn't all her Aura.