I recommend creating a theme file with all the colors and background images. Then use gpedit.msc to load the specific theme:
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According to THE SOP, the XML file has been modified, but it has not taken effect, the color has not been changed to black, and the theme has not been changed to dark mode
<Themes>
<ThemeName>Fabrikam Theme</ThemeName>
<DefaultThemesOff>false</DefaultThemesOff>
<DesktopBackground>%WINDIR%\OEM\CustomizationFiles\Theme1\fabrikam-wallpaper.jpg</DesktopBackground>
<BrandIcon>%WINDIR%\OEM\CustomizationFiles\Theme1\fabrikam-logo.png</BrandIcon>
<WindowColor>0xFF000000</WindowColor>
<UWPAppsUseLightTheme>false</UWPAppsUseLightTheme>
</Themes>
I recommend creating a theme file with all the colors and background images. Then use gpedit.msc to load the specific theme: