Fix ProgressBar dark mode rendering inconsistency across style variants

src/System.Windows.Forms/System/Windows/Forms/Controls/ProgressBar/ProgressBar.cs

@@ -26,6 +26,7 @@ public partial class ProgressBar : Control
     private int _marqueeAnimationSpeed = 100;
 
     private static readonly Color s_defaultForeColor = SystemColors.Highlight;
+    private static readonly Color s_defaultDarkModeBackColor = SystemColors.ControlText;
 
     private ProgressBarStyle _style = ProgressBarStyle.Blocks;
 
@@ -74,26 +75,6 @@ protected override CreateParams CreateParams
     protected override void OnCreateControl()
     {
         base.OnCreateControl();
-
-        // If SystemColorMode is enabled, we need to disable the Visual Styles
-        // so Windows allows setting Fore- and Background color.
-        // There are more ideal ways imaginable, but this does the trick for now.
-
-        if (Application.IsDarkModeEnabled)
-        {
-            if (!ShouldSerializeBackColor())
-            {
-                BackColor = SystemColors.ControlDarkDark;
-            }
-
-            if (!ShouldSerializeForeColor())
-            {
-                ForeColor = SystemColors.Highlight;
-            }
-
-            // Disables Visual Styles for the ProgressBar.
-            PInvoke.SetWindowTheme(HWND, " ", " ");
-        }
     }
 
     [Browsable(false)]
@@ -133,6 +114,8 @@ public ProgressBarStyle Style
                 if (IsHandleCreated)
                 {
                     RecreateHandle();
+                    // Re-apply theming after handle recreation
+                    ApplyTheming();
                 }
 
                 if (_style == ProgressBarStyle.Marquee)
@@ -349,7 +332,8 @@ protected override void OnBackColorChanged(EventArgs e)
         base.OnBackColorChanged(e);
         if (IsHandleCreated)
         {
-            PInvokeCore.SendMessage(this, PInvoke.PBM_SETBKCOLOR, 0, BackColor.ToWin32());
+            ApplyTheming();
+            PInvokeCore.SendMessage(this, PInvoke.PBM_SETBKCOLOR, 0, GetEffectiveBackColor().ToWin32());
         }
     }
 
@@ -358,7 +342,8 @@ protected override void OnForeColorChanged(EventArgs e)
         base.OnForeColorChanged(e);
         if (IsHandleCreated)
         {
-            PInvokeCore.SendMessage(this, PInvoke.PBM_SETBARCOLOR, 0, ForeColor.ToWin32());
+            ApplyTheming();
+            PInvokeCore.SendMessage(this, PInvoke.PBM_SETBARCOLOR, 0, GetEffectiveForeColor().ToWin32());
         }
     }
 
@@ -603,13 +588,17 @@ public void Increment(int value)
     protected override void OnHandleCreated(EventArgs e)
     {
         base.OnHandleCreated(e);
+
+        ApplyTheming();
+
         if (IsHandleCreated)
         {
             PInvokeCore.SendMessage(this, PInvoke.PBM_SETRANGE32, (WPARAM)_minimum, (LPARAM)_maximum);
             PInvokeCore.SendMessage(this, PInvoke.PBM_SETSTEP, (WPARAM)_step);
             PInvokeCore.SendMessage(this, PInvoke.PBM_SETPOS, (WPARAM)_value);
-            PInvokeCore.SendMessage(this, PInvoke.PBM_SETBKCOLOR, (WPARAM)0, (LPARAM)BackColor);
-            PInvokeCore.SendMessage(this, PInvoke.PBM_SETBARCOLOR, (WPARAM)0, (LPARAM)ForeColor);
+
+            PInvokeCore.SendMessage(this, PInvoke.PBM_SETBKCOLOR, 0, GetEffectiveBackColor().ToWin32());
+            PInvokeCore.SendMessage(this, PInvoke.PBM_SETBARCOLOR, 0, GetEffectiveForeColor().ToWin32());
         }
 
         StartMarquee();
@@ -703,8 +692,46 @@ private void UserPreferenceChangedHandler(object o, UserPreferenceChangedEventAr
     {
         if (IsHandleCreated)
         {
-            PInvokeCore.SendMessage(this, PInvoke.PBM_SETBARCOLOR, 0, ForeColor.ToWin32());
-            PInvokeCore.SendMessage(this, PInvoke.PBM_SETBKCOLOR, 0, BackColor.ToWin32());
+            ApplyTheming();
+
+            PInvokeCore.SendMessage(this, PInvoke.PBM_SETBARCOLOR, 0, GetEffectiveForeColor().ToWin32());
+            PInvokeCore.SendMessage(this, PInvoke.PBM_SETBKCOLOR, 0, GetEffectiveBackColor().ToWin32());
+        }
+    }
+
+    private Color GetEffectiveBackColor()
+    {
+        if (ShouldSerializeBackColor())
+        {
+            return BackColor;
+        }
+
+        return Application.IsDarkModeEnabled ? s_defaultDarkModeBackColor : SystemColors.Control;
+    }
+
+    private Color GetEffectiveForeColor()
+    {
+        if (ShouldSerializeForeColor())
+        {
+            return ForeColor;
+        }
+
+        return s_defaultForeColor;
+    }
+
+    private void ApplyTheming()
+    {
+        if (!IsHandleCreated)
+        {
+            return;
+        }
+
+        if (Application.IsDarkModeEnabled || ShouldSerializeBackColor() || ShouldSerializeForeColor())
+        {
+            // In dark mode on newer Windows builds, style switching can produce mixed rendering
+            // across Blocks/Continuous/Marquee. Disable visual styles and drive colors via PBM_SET*COLOR
+            // for consistent appearance.
+            PInvoke.SetWindowTheme(HWND, " ", " ");
         }
     }