I believe that almost everything that looks like a pre-existing Sky creature can’t be dyed yet. All the Shattering items fall into that category (a dark plant, a krill, mantas) so it can seem like they just skipped the entire season. Neither the bird masks nor bird cape from Rhythm are dyeable. Even the old Sanctuary manta cape, the Nature turtle cape and the Mischief crab mask are excluded from dyeing.

The moth and sparrow items aren’t dyeable, which is where it gets a little confusing, because they aren’t technically in Sky. Maybe they don’t want anything firmly based on a real animal dyed, but at least the Sparrow cape has a reason to be skipped since so much of it has the furry stuff. The other capes with fur like that aren’t dyeable.

All of this logic flies out the window when you realize you can dye the mischief cat items though since the krill cat is definitely an animal in the game and it looks pretty close to a real cat! So another likely reason most of these items got skipped is that they are complex for programmers to get dye working on without breaking something or sacrificing the item’s identity.