Blue Accent Color Pref Doesn't Work

### Describe the bug

Setting "userChrome.theme.proton_color.dark_blue_accent" to true in the user.js does not change the accent color for the Bookmark icon or the Download icon on the toolbar after relaunching in any dark mode theme.

### Expected behavior

Accent color should be changed from cyan to blue upon setting the pref and relaunching.

### Screenshots

_No response_

### OS

Windows 10

### OS - Others

_No response_

### Firefox Version

120

### Distribution

- [ ] [Original Lepton](https://github.com/black7375/Firefox-UI-Fix)
- [ ] [Lepton's photon style](https://github.com/black7375/Firefox-UI-Fix/tree/photon-style)
- [X] [Lepton's proton style](https://github.com/black7375/Firefox-UI-Fix/tree/proton-style)

### Theme

- [ ] Light
- [X] Dark
- [ ] Alpenglow (System: Light)
- [ ] Alpenglow (System: Dark)
- [X] System Default
- [X] Others: (e.g. [Photon Colors](https://addons.mozilla.org/en-US/firefox/addon/photon-colors/), [Google Chrome Dark](https://addons.mozilla.org/en-US/firefox/addon/google-chrome-dark/), [Fairytale Of Nature](https://addons.mozilla.org/en-US/firefox/addon/fairytale-of-nature/))

### Theme - More Info

_No response_

### Additional context

_No response_

Start by tracing the SCSS and userChrome preference handling for "userChrome.theme.proton_color.dark_blue_accent" in the proton-style UI. Reproduce the issue on Firefox 120 with a dark theme and the preference enabled, then verify that the Bookmark and Download toolbar icons change from cyan to blue after relaunch.

Written by the indexing model from the issue text.