I'm sure people have raised this issue before, but I feel like now is a great time to mention it because there's a really prominent example in the Sept. 15 update.
The Etherbound Back+Glider set is back at the Statuette dealer for 60 thingies (which I would classify as, like, the "fancy" tier). You can dye the glider. It's absolutely beautiful! Only two channels, but whatever dye you assign to the energy part will create some really nice gradations of color in the wings. The base plate looks really good with a high-contrast dye (like Darkness or Searing) as well. It's got a solid "opening" animation, too, with a pretty smooth transition from backpiece to glider, which is always what you want in a combo set like this. Dang nice glider all around.
But… you can't dye the matching backpiece. So if you want to use them together, you're basically stuck with the brass + purple colorscheme.
I understand why this happened: this design is from before any backpieces were dyeable. But, these days, it's such an annoying little historical wart that's holding back a lot of really nice skins, and probably a bit of a nasty surprise for newer players the first time they buy one of these legacy skins. I'd love it if someone on the art team could fix up the biggest offenders in this category; hopefully it's not that difficult given that the glider versions already have pre-opening shapes with all their dye channels set.