I may be missing the mark, but I think those two armour sets came out before any of the Slumber-themed lockboxes did, since I've definitely noticed that they're definitely way less neon-y and it makes looking for same-themed accessories for them pretty darn hard, and if my memory of box releases is correct, the success of various Tech-Themed cosmetics may've lead to Slumber being just as bright whilst the original two equipment pieces weren't meant to be by design.

I think it's an unfortunate case of two different themes introduced at different times, but they're meant to be the same and it's really abrasive. The easy option would be to just update the Starlit Mail and Hunting stuff to be in line with Slumber, but I personally enjoy the two armour sets how they are as they feel aesthetically diegetic with every other armour in the game and that they expand on the theme more. Out of all the Cosmetic-centric themes, I think only Shadow has been able to escape it with the Snarbolax and Shade armour sets. I may have missed some other exceptions though.

tangent-note though, there's definitely some odd choices with theming though, since the Quicksilver armour as a whole jumps between three different themes per upgrade (Toasty -> Heavy -> Volcanic), and there's realistically no easy way any Divine cosmetics are matching the Kat Eye stuff as it lacks the gold that Divine's primarily made of. Naturally...I don't think some of this can be fixed easily.