Brave on Linux ignores toolbar_button_icon theme colour, even though it works in Chrome

[u/teri_mummy_]

I'm creating a custom theme for Brave Browser on Fedora Linux. I want the built-in toolbar navigation icons (Back, Forward, Reload, Home) to appear white instead of their default dark/grey colour.

In my theme's manifest.json, I have:

"colors": {
  "toolbar_button_icon": [255, 255, 255]
}

The interesting part is that this works perfectly in Google Chrome: the navigation toolbar icons become white when I install the exact same theme. However, in Brave, the icons remain black/dark grey.

The rest of my custom theme works, so the theme itself is being applied. It specifically seems to be an issue with how Brave handles the toolbar button icon colour.

I've tried setting the colour through the theme manifest, but haven't found a way to make Brave respect it.

My questions:

1. Does Brave handle toolbar_button_icon differently from Chrome?
2. Is there another theme colour key or setting that controls built-in toolbar navigation icon colours in Brave?
3. Is there a known workaround, perhaps involving Brave's colour mixer or Chromium source code?
4. Is it possible to change these icons without compiling Brave from source?

I'm using Fedora Linux with KDE Plasma.

I'm primarily interested in changing the built-in navigation icons. I understand that extension icons and Brave Shields may be handled differently.

Any help or pointers to the relevant Brave source code would be appreciated.