True, although not in the same way. KDE is using its own GTK theme and uses ~/.config/gtk-3.0/gtk.css to override colors to the accent color. But this method is broken for sandboxed versions of Firefox since they can't access ~/.config/gtk-3.0/gtk.css (though with flatpak you could create an override to allow it).
I believe (and hope) Firefox is now following the standardized accent color portal for determining the accent color. If so, then this accent color change should work on Gnome, KDE, Pantheon, and other desktops that support the accent color portal. If true, then even sandboxed apps should follow the accent color without messing with the sandbox.
I love the flatpak Wayland portals and systemd desktop stack. It allows Linux to finally have some sort of standard that everyone agrees on. This is what has been holding Linux back for so many years, it's basically impossible to build a Linux app that will work for everyone because of this. Now we have a single dedicated system APIs that is available basically everywhere
Stupid question, Do you know if there is a similar method for qt apps installed through flatpak? I could not get Kate to use my accent color and it's been driving me crazy. Also, happy we finally have a standard for accent colors. Now if we could just have a standard for global menus, probably wishful thinking.
This is just extremely misleading. Libadwaita uses the system accent color by default which makes it even easier respect the users preference when developing a GTK application.
Now if they can fix the bug where once in a while I click to a tab and it doesn't switch to it unless I minimize and maximize again, and needing a restart of the browser to get rid of that behavior...