Inherit Windows accent color

src/MaterialDesignColors.Wpf/MaterialDesignColor.cs

@@ -2,6 +2,7 @@
 
 public enum PrimaryColor
 {
+    Inherit,
     Red = MaterialDesignColor.Red500,
     Pink = MaterialDesignColor.Pink500,
     Purple = MaterialDesignColor.Purple500,
@@ -25,6 +26,7 @@ public enum PrimaryColor
 
 public enum SecondaryColor
 {
+    Inherit,
     Red = MaterialDesignColor.RedSecondary,
     Pink = MaterialDesignColor.PinkSecondary,
     Purple = MaterialDesignColor.PurpleSecondary,

src/MaterialDesignThemes.Wpf/BundledTheme.cs

@@ -1,4 +1,5 @@
-using MaterialDesignColors;
+using System.Windows.Media;
+using MaterialDesignColors;
 
 namespace MaterialDesignThemes.Wpf;
 
@@ -10,9 +11,8 @@ public BaseTheme? BaseTheme
         get => _baseTheme;
         set
         {
-            if (_baseTheme != value)
+            if (SetField(ref _baseTheme, value))
             {
-                _baseTheme = value;
                 SetTheme();
             }
         }
@@ -62,17 +62,35 @@ public ColorAdjustment? ColorAdjustment
 
     private void SetTheme()
     {
-        if (BaseTheme is BaseTheme baseTheme &&
-            PrimaryColor is PrimaryColor primaryColor &&
-            SecondaryColor is SecondaryColor secondaryColor)
+        if (BaseTheme is not BaseTheme baseTheme ||
+            PrimaryColor is not PrimaryColor primaryColor ||
+            SecondaryColor is not SecondaryColor secondaryColor)
         {
-            Theme theme = Theme.Create(baseTheme,
-                SwatchHelper.Lookup[(MaterialDesignColor)primaryColor],
-                SwatchHelper.Lookup[(MaterialDesignColor)secondaryColor]);
-            theme.ColorAdjustment = ColorAdjustment;
-
-            ApplyTheme(theme);
+            return;
         }
+
+        // only perform the registry lookup if needed, and only once
+        Lazy<Color?> accentColor = new(Theme.GetSystemAccentColor);
+
+        Color colorPrimary = primaryColor == MaterialDesignColors.PrimaryColor.Inherit
+                              ? (accentColor.Value ?? SwatchHelper.Lookup.First().Value)
+                              : SwatchHelper.Lookup[(MaterialDesignColor)primaryColor];
+
+        Color colorSecondary = secondaryColor == MaterialDesignColors.SecondaryColor.Inherit
+                              ? (accentColor.Value ?? SwatchHelper.Lookup.First().Value)
+                              : SwatchHelper.Lookup[(MaterialDesignColor)secondaryColor];
+
+        Theme theme = Theme.Create(baseTheme, colorPrimary, colorSecondary);
+        theme.ColorAdjustment = ColorAdjustment;
+
+        ApplyTheme(theme);
+    }
+
+    protected bool SetField<T>(ref T field, T value)
+    {
+        if (EqualityComparer<T>.Default.Equals(field, value)) return false;
+        field = value;
+        return true;
     }
 
     protected virtual void ApplyTheme(Theme theme) =>

src/MaterialDesignThemes.Wpf/Theme.cs

@@ -1,4 +1,5 @@
-using System.Windows.Media;
+using System.Diagnostics;
+using System.Windows.Media;
 using MaterialDesignColors;
 using Microsoft.Win32;
 
@@ -31,6 +32,44 @@ public partial class Theme
         }
     }
 
+    /// <summary>
+    /// Get the current Windows accent color.
+    /// Based on ControlzEx
+    /// https://github.com/ControlzEx/ControlzEx/blob/48230bb023c588e1b7eb86ea83f7ddf7d25be735/src/ControlzEx/Theming/WindowsThemeHelper.cs#L53
+    /// </summary>
+    /// <returns></returns>
+    public static Color? GetSystemAccentColor()
+    {
+        Color? accentColor = null;
+
+        try
+        {
+            var registryValue = Registry.GetValue(@"HKEY_CURRENT_USER\Software\Microsoft\Windows\DWM", "ColorizationColor", null);
+
+            if (registryValue is null)
+            {
+                return null;
+            }
+
+            // We get negative values out of the registry, so we have to cast to int from object first.
+            // Casting from int to uint works afterwards and converts the number correctly.
+            var pp = (uint)(int)registryValue;
+            if (pp > 0)
+            {
+                var bytes = BitConverter.GetBytes(pp);
+                accentColor = Color.FromArgb(bytes[3], bytes[2], bytes[1], bytes[0]);
+            }
+
+            return accentColor;
+        }
+        catch (Exception exception)
+        {
+            Trace.TraceError(exception.ToString());
+        }
+
+        return accentColor;
+    }
+
     public static Theme Create(BaseTheme baseTheme, Color primary, Color secondary)
     {
         Theme theme = new();