True. Castle...do a search on Qpub for it. Lots of posts about red castle and green castle. Many of us, back when these were posted, speculated red castle was the army corp of engineers, as their logo is a red castle, and they were gonna be used to build the wall.  But this doesnt explain green castle. So more likely, castle is a unit, and red or green is a stop or go sign.  I also cant help but wonder if castle is a reference to 'the man in the high castle' (a book and series on amazon, amazing show)  The reason I wonder this is because Q is essentially playing the role of the man in the high castle. You have to watch the show to get it.