This doesn't really seem that important of a suggestion, like new weapons, new sprites, or dual wiel- [shot], but Spiral Knights is a game about variety right?
There's a hell of a lot of colour schemes out there, and you guys at this point are probably like "this is a GAME not a WARDROBE" or whatever, but I suggest adding a new colour scheme.
Oceanic, a mix of turquoise, light blue, and violet-grey.
Examples.
Haven't really seen a lot of things like this, and a different colour scheme would liven things up a tiny bit. Plus you could make a new promotion, right Thr- [shot again].
Plenty of people think that "huge sword/gun/swordgun > looks", but I think that having a good variety of looks makes a game look slightly better.