Apply dark theme through user policy

scripts/Set-SguDomainUserPolicies.ps1

@@ -10,6 +10,7 @@ $ErrorActionPreference = 'Stop'
 $policyKey = 'HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\System'
 $policyValueName = 'DisableLockWorkstation'
 $desktopPolicyKey = 'HKCU\Software\Policies\Microsoft\Windows\Control Panel\Desktop'
+$themeKey = 'HKCU\Software\Microsoft\Windows\CurrentVersion\Themes\Personalize'
 
 $identity = [Security.Principal.WindowsIdentity]::GetCurrent()
 $principal = [Security.Principal.WindowsPrincipal]::new($identity)
@@ -83,6 +84,19 @@ if ($PSCmdlet.ShouldProcess($GpoName, 'Prevent SGU users from manually locking w
         -Type String `
         -Value '0' | Out-Null
 
+    # Apply the native Windows dark theme at user logon. Both values are required:
+    # one controls the shell and the other controls supported applications.
+    foreach ($themeValueName in 'AppsUseLightTheme', 'SystemUsesLightTheme') {
+        Set-GPRegistryValue `
+            -Name $GpoName `
+            -Domain $domainName `
+            -Server $DomainController `
+            -Key $themeKey `
+            -ValueName $themeValueName `
+            -Type DWord `
+            -Value 0 | Out-Null
+    }
+
     if ($WallpaperPath) {
         Set-GPRegistryValue `
             -Name $GpoName `
@@ -115,6 +129,18 @@ $screenSaverValue = Get-GPRegistryValue `
     -Server $DomainController `
     -Key $desktopPolicyKey `
     -ValueName 'ScreenSaveActive'
+$appsThemeValue = Get-GPRegistryValue `
+    -Name $GpoName `
+    -Domain $domainName `
+    -Server $DomainController `
+    -Key $themeKey `
+    -ValueName 'AppsUseLightTheme'
+$systemThemeValue = Get-GPRegistryValue `
+    -Name $GpoName `
+    -Domain $domainName `
+    -Server $DomainController `
+    -Key $themeKey `
+    -ValueName 'SystemUsesLightTheme'
 $link = @(Get-GPInheritance -Target $TargetOuDn -Domain $domainName -Server $DomainController).GpoLinks |
     Where-Object DisplayName -eq $GpoName |
     Select-Object -First 1
@@ -138,5 +164,6 @@ if ($WallpaperPath) {
     LinkEnabled = [bool]$linkEnabled
     DisableLockWorkstation = [int]$configuredValue.Value
     ScreenSaverDisabled = [string]$screenSaverValue.Value -eq '0'
+    DarkMode = ([int]$appsThemeValue.Value -eq 0) -and ([int]$systemThemeValue.Value -eq 0)
     Wallpaper = $configuredWallpaper
 }