I agree with this a ton! ESPECIALLY considering one of the earliest pieces of glamour you can get in the game is the "White Beret" - which is not locked to being white!
The Thavnairian Ribbon (and the Sharlayan Diadema) are extra egregious to me, considering just how much work you need to do to even access them (and then 800 bicolor gemstones a pop!) only for them to not be dyeable? I can almost understand the Diadema, since it's, y'know, grapes, but the Thavnairian Ribbon? The ribbon from Thavnair - the singularly MOST COLORFUL CITY in the game??
Both should be able to be dyed, though. For the diadema I think it would be neat to be able to dye the grapes to other colors to be able to mimic other fruit. Red would make a great imitation holly wreath, and blue could make them into blueberries!