Some backpack items are not dyeable while their respective glider versions are

For example, those that I know of (and own): Scaled Dragon Wings Backpack, Moth Wings Backpack, Largos Fin Backpack skins are not dyeable. But their glider versions are.So it should be easy to change back skins into dyeable versions, I hope? It's important in fashion wars if there are more options for colouring.Please make it possible to dye these backpack skins! Thank you for reading.

Unlikely to happen per: https://www.guildwars2.com/en/news/wrap-yourself-in-an-emblazoned-cape/

While we cannot add dye channels to existing backpieces, keep an eye out for dyeable backpacks of different styles in the future!

ANet never looks back at these things, can't monetize what has already been sold I guess.

Also, AP backpieces need gliders and should be dyable. The AP armors as well should have some dye slots. But again, ANet never looks back at these things. They don't care.

That's a bit disingenuous to say that they don't care. They've said that these things weren't coded/designed to be dye-able from the start and that making them would take a lot of resources. They seem to have decided that the cost outweighs the benefit of going back to make changes rather than working to move forward.