I dont think that there was much of a librarium before the council of nikea, so I would assume that the Librarians would wear the same armour as their other brothers. Also, this may be speculation, but in the second DA HH novel (I cannot think of the name at the moment) The use of psychic hoods was in its infancy and not all librarians had one.
I thought any mutations whatsoever like that were banned outright so there were no psykers in the space marines, apart from the primarchs. The ships astropaths were there but I am fairly sure Librarians were not allowed in legions. Isn't that why the thousand sons were attacked? they used their psychic powers and the emperor thought i to be wrong??
One could also argue that the other Legions would have chosen not to follow the sanctions at Nikea, considering there has been shown a presence of Librarians in loyalist legions after the events at Nikea in the overall timeline (Dark Angel series of books, for example.
Also, in A Thousand Sons you see that there is no collective Librarium, and that the Librarians are trained in-house. Considering the Blue of the Librarians come from the Librarium as the Red of the Techmarines comes from the Ad-Mech, I would assume they would retain their original legion color.
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