User interface in Night sky theme in Windows

[PtJade-Ceramic]

Issue type

UI bug (incorrect info or interface appearance)

Description with steps to reproduce

The user interface is white when it follows the system theme set as Night sky in Windows.

1. Turn the high contrast mode on in Windows.
2. Select the theme Night sky from the Contrast themes drop-down menu.
   
3. Open MuseScore Studio 4.
4. Go to Appearance.
5. Toggle Follow the system theme in High contrast theme.
6. The theme is automatically set to White instead of Black.

Supporting files, videos and screenshots

Effect when the system theme is set to Night sky:

What is the latest version of MuseScore Studio where this issue is present?

OS: Windows 11 Version 2009 or later, Arch.: x86_64, MuseScore Studio version (64-bit): 4.5.1-250800846, revision: github-musescore-musescore-603eca8

Regression

No.

Operating system

Version Windows 11 Home
Version number 24H2 OS
Internal version 26100.3476
Experience Windows Function experience package 1000.26100.54.0

Additional context

Some other issues on dark/night mode

MuseScore Studio design team task

The UI color system is missing a grey that feels like a mid-grey both in light and dark themes.

This would be useful for cases in illustrations that are affected by light/dark/high-contrast mode where we want to "dim" something without relying on opacity or the score color variables (which do not change between light/dark mode).

As an example: the X in the Open/Atonal element in Palettes > Key signatures used to use the score "Formatting color" variable, which became an issue when we made it pink. Now, it's grey again but uses a score variable added in this PR, so it can't be different in light/dark/high-contrast modes.

Originally posted by @avvvvve in #26331

@jessjwilliamson we should probably make sure this gets updated when we update the imagery here in 4.5.

Originally posted by @bkunda in #25239

Checklist

• This report follows the guidelines for reporting bugs and issues
• I have verified that this issue has not been logged before, by searching the issue tracker for similar issues
• I have attached all requested files and information to this report
• I have attempted to identify the root problem as concisely as possible, and have used minimal reproducible examples where possible