Linux host VBox 5.1.18 ignores GTK color theme -> Qt5 issue

[jamshark70]

Ubuntu 14.04. I'm using "Dorian-theme"[1]. In just about every application, I get dark window title bars, menu bars, dialog box backgrounds etc.

When I was using VirtualBox 4.x, VBox menu bars and backgrounds were dark, matching the theme.

I recently upgraded to 5.1, and backgrounds have regressed to light color.

It's not a high priority issue, but it's jarring to have two brightly colored bars (VBox menus "File, Machine...", and the VBox status bar at the bottom) on the screen where everything else is dark.

Since VBox used to be able to handle color themes properly, and now it doesn't, technically it's a regression.

Attached is a screenshot showing Firefox menu bars (OK) vs. VBox (not OK).

[1] ​https://www.gnome-look.org/content/show.php/Dorian+Theme?content=157200

[jamshark70]

Firefox menu bars (correct colors) vs VBox menu bar (bright, wrong colors)

[Michael Thayer]

I think that this is not a regression as such but more limited support for older Linux systems in newer versions. More specifically, we require a reasonably recent version of Qt5, and if a particular distribution does not provide that by default we bundle a package. However, bundled versions of Qt5 are not (as far as I know) able to pick up theme information. I don't think it would be impossible, but unless we have missed something it is just not supported by Qt. You might want to get in touch with the Qt developers about that. It is something they could probably fix if they wanted to, or someone else could fix using the Qt source if they did not. Unfortunately it is something we will not be able to do, as we have too many tasks which we consider more important which take up our available developer time.