Today in the Test Realm I purchased the Sidhe Attire (the robes with the Astral symbols) thinking that if they could be dyed blue and green they'd go quite nicely with the Silent Nightcap. Sadly I found that they cannot have their colors changed. :-(
It is my humble request as an avid and loyal player of W101 for this feature to be re-enabled for not only the Sidhe Attire, but all of the Sidhe items that are on sale for 12,500 Crowns apiece. I find it odd and ironic that all of the retired Astral garments of the past can be dyed, and the more recent Elven Attire as well, which is also of the same base uniform (Whimsical Cap/Robe/Boots).
I wish I could give you a better reason to do this than just because I would love it if it happened, but I can tell you I'd definitely purchase the robes in the Live Realm if this became a reality!