How Do I Change WS Screen Colors ?

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wireshark -platform windows:darkmode=2

Dark mode for Windows is a work in progress.
Of the three win10 machines I tested on, it worked on win10 1809 and win10 1909.
No luck on win10 2004 but didn't really dig into what was going on there.

Background info and steps to use in this issue: 16221 - Dark mode support on Windows 10 and later

Wireshark dev guide mentions that it uses Qt library: 12.2.4.6. Colors And Themes

Wireshark supports dark themes (aka “dark mode”) on some platforms. We leverage Qt’s dark theme support when possible, but have implemented our own support and workarounds in some cases."

(-platform is not a Wireshark option. It is passed through to the Qt libraries: QGuiApplication Class)

You can specify platform-specific arguments for the -platform option. Place them after the platform plugin name following a colon as a comma-separated list. For example, -platform windows:dialogs=xp,fontengine=freetype.

darkmode=[1|2] controls how Qt responds to the activation of the Dark Mode for applications introduced in Windows 10 1903 (since Qt 5.15).
A value of 1 causes Qt to switch the window borders to black when Dark Mode for applications is activated and no High Contrast Theme is in use. This is intended for applications that implement their own theming.

A value of 2 will in addition cause the Windows Vista style to be deactivated and switch to the Windows style using a simplified palette in dark mode. This is currently experimental pending the introduction of new style that properly adapts to dark mode.

Windows 10 colors are set by the Colors and Themes options in the Personalisation option in Settings.

The Wireshark colors that are modifiable are set in the Preferences -> Fonts and Colors dialog.