Are there any books that explain this? UESP says that it's because the Blades originated from the Akaviri Dragonguard, which would explain why they wear Akaviri stuff even though their loyalties lie with the Empire. What I don't get is why they decided that that part of their past is important all of a sudden? They seem to identify themselves a little bit too much with dragonhunters. Is this only a facade to get the Dragonborn to work for them and be able to recruit people into the Blades and to pose as heroes for the populace, playing on their fear of the new Dragon threat?