For the sake of accessories, if other reasons don't work, is there a chance to have at least metal parts of gunslinger hats adjusted so they fit colour theme of armours?
Something like this.

In case of helm accessories (like helm-mounted display) as long as Cool ones look all right with Nameless Hat, Fancy ones don't really fit Justifier Hat and Volcanic ones look just awkward on Shadowsun Stetson.

Off topic side note:
Also, since I've already started one of those gunslinger issue threads, may I suggest Piercing path for Antigua not to be made as shadow themed item? My personal preference aside, none of gunslinger armour/hats follow shadow theme. The original themes of SK are far better then shadow theme, so don't overuse it on every possible item please. Maybe, since beasts are vulnerable to piercing, something inspired by a famous hunter, like Quatermain, would be more suitable. I can imagine a gun with barrel wrapped in a piece of fur with leopard-like marks. Or maybe some fancy anti-fiendish exorcist gun?