Problem

Experienced this on my local setup (DMS + Niri), the GTK4 color-scheme refresh introduced in #1643 does not work correctly.

default as intermediate toggle value

refreshGTK4() currently toggles through default when the current scheme is prefer-dark:

if current == "prefer-dark" {
    toggle = "default"  // ← problematic
} else {
    toggle = "prefer-dark"
}

It seems on niri, default is not treated the same as on GNOME — it may not trigger the GTK4 style reload that the toggle is meant to force. Using prefer-light as the intermediate value is explicit and unambiguous, and produces the same toggling effect.

dconf write is more universal: it writes directly to the DConf database without needing schema definitions, and is available on virtually any system that runs GTK apps.

This was already noted in the comments on #1643:

Now that I think about it, we should use dconf write /org/gnome/desktop/interface/color-scheme '"prefer-light"' instead of gsettings, because it is an "universal" way of doing it. For example, in NixOS it is a pain to setup gsettings schemas, and some minimalistic distro won't include it, however dconf probably is universal, or at least much more common.

Proposed Fix

• Replace "default" with "prefer-light" as the intermediate toggle value in refreshGTK4() and as the scheme value in syncColorScheme() for light mode.
• Add a DconfSet utility that tries dconf write first (falling back to gsettings), and use it for all color-scheme writes.

A pull request with the fix is attached.