[Bug]: Flatpak applications do not obey system accent color

[tornupnegatives]

Checklist

• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the issue tracker for a bug that matches the one I want to file, without success.
• If this is an issue with a particular app, I have tried filing it in the appropriate issue tracker for the app (e.g. under https://github.com/flathub/) and determined that it is an issue with Flatpak itself.
• This issue is not a report of a security vulnerability (see here if you need to report a security issue).

Flatpak version

1.14.4

What Linux distribution are you using?

Ubuntu

Linux distribution version

23.10

What architecture are you using?

x86_64

How to reproduce

1. Set the system accent color from Settings > Appearance > Color
2. Launch any Flatpak application

Expected Behavior

The accent color for UI elements such as the fill of switches or the mouseover highlight color should match the system theme

Actual Behavior

The accent color for UI elements is a high-contrast blue

Additional Information

I have experienced this problem on Ubuntu 22.04 LTS as well. I tried to copy the contents of /usr/share/themes to ~/.themes and set filesystem overrides and GTK_* variables through the flatpak CLI, to no avail.

[chrisawi]

As best I can tell, Ubuntu has made accent color variants of Yaru, some of which are available as GTK3 theme extensions on Flathub. For the colors where those extensions exist, they would be installed automatically by flatpak update, but that doesn't help GTK4/Libadwaita apps. Ubuntu has apparently patched their libadwaita package, and without a similar change in the GNOME runtime (which isn't going to happen), I don't think there's any override that could make Ubuntu's accent color work for flatpak. The best you could do is override the stylesheet with something like Gradience.

There is a plan for upstream accent color support using a portal setting, but that is still in progress (and seems stalled).

I don't think there's any flatpak bug here; all of the work needed for accent colors is elsewhere in the stack.

[tornupnegatives]

@chrisawi Gotcha. Thanks for the background. For now, I'll try my hand at converting the stock Yaru themes to a format usable with Gradience. Hopefully upstream accent color support gets merged!