VMPK already honors the system settings for dark modes in macOS and Linux operating systems. Since October 2018, Windows has support for dark mode as well, via the Colors settings in Control Panel.
There is an open ticket in Qt's tracker requesting this feature. Until it is solved, this ticket is a reminder.
When the system setting is not useful, there is a configuration option to force a dark mode theme in Preferences dialog -> Visualization -> Forced Dark Mode.
Last edit: Pedro Lopez-Cabanillas 2022-03-27
ticket QTBUG-72028 is now closed in Qt 6.5