Fix ProgressBar dark mode rendering inconsistency across style variants

src/System.Windows.Forms/PublicAPI.Shipped.txt

@@ -1606,7 +1606,6 @@ override System.Windows.Forms.ProgressBar.DoubleBuffered.set -> void
 override System.Windows.Forms.ProgressBar.Font.get -> System.Drawing.Font!
 override System.Windows.Forms.ProgressBar.Font.set -> void
 override System.Windows.Forms.ProgressBar.OnBackColorChanged(System.EventArgs! e) -> void
-override System.Windows.Forms.ProgressBar.OnCreateControl() -> void
 override System.Windows.Forms.ProgressBar.OnForeColorChanged(System.EventArgs! e) -> void
 override System.Windows.Forms.ProgressBar.OnHandleCreated(System.EventArgs! e) -> void
 override System.Windows.Forms.ProgressBar.OnHandleDestroyed(System.EventArgs! e) -> void

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;
 
@@ -71,31 +72,6 @@ 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)]
     [EditorBrowsable(EditorBrowsableState.Never)]
     public override bool AllowDrop
@@ -133,6 +109,8 @@ public ProgressBarStyle Style
                 if (IsHandleCreated)
                 {
                     RecreateHandle();
+                    // Re-apply theming after handle recreation
+                    ApplyTheming();
                 }
 
                 if (_style == ProgressBarStyle.Marquee)
@@ -349,7 +327,7 @@ protected override void OnBackColorChanged(EventArgs e)
         base.OnBackColorChanged(e);
         if (IsHandleCreated)
         {
-            PInvokeCore.SendMessage(this, PInvoke.PBM_SETBKCOLOR, 0, BackColor.ToWin32());
+            PInvokeCore.SendMessage(this, PInvoke.PBM_SETBKCOLOR, 0, GetEffectiveBackColor().ToWin32());
         }
     }
 
@@ -358,7 +336,7 @@ protected override void OnForeColorChanged(EventArgs e)
         base.OnForeColorChanged(e);
         if (IsHandleCreated)
         {
-            PInvokeCore.SendMessage(this, PInvoke.PBM_SETBARCOLOR, 0, ForeColor.ToWin32());
+            PInvokeCore.SendMessage(this, PInvoke.PBM_SETBARCOLOR, 0, GetEffectiveForeColor().ToWin32());
         }
     }
 
@@ -603,13 +581,17 @@ 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();
@@ -701,10 +683,56 @@ private void UpdatePos()
     /// </remarks>
     private void UserPreferenceChangedHandler(object o, UserPreferenceChangedEventArgs e)
     {
-        if (IsHandleCreated)
+        if (!IsHandleCreated)
+        {
+            return;
+        }
+
+        // Only react to changes that can affect colors or theme changes.
+        if (e.Category is not UserPreferenceCategory.Color and not UserPreferenceCategory.General)
+        {
+            return;
+        }
+
+        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 : BackColor;
+    }
+
+    private Color GetEffectiveForeColor()
+    {
+        return ShouldSerializeForeColor() ? ForeColor : s_defaultForeColor;
+    }
+
+    private void ApplyTheming()
+    {
+        if (!IsHandleCreated)
+        {
+            return;
+        }
+
+        if (Application.IsDarkModeEnabled)
+        {
+            // 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, " ", " ");
+        }
+        else
         {
-            PInvokeCore.SendMessage(this, PInvoke.PBM_SETBARCOLOR, 0, ForeColor.ToWin32());
-            PInvokeCore.SendMessage(this, PInvoke.PBM_SETBKCOLOR, 0, BackColor.ToWin32());
+            // Restore default theming when dark mode and custom colors are no longer active.
+            PInvoke.SetWindowTheme(HWND, (PCWSTR)null, (PCWSTR)null);
         }
     }
 

src/test/unit/System.Windows.Forms/System/Windows/Forms/ProgressBarTests.cs

@@ -2165,6 +2165,69 @@ public void ProgressBar_OnHandleCreated_InvokeWithHandle_CallsHandleCreated(Prog
         Assert.True(control.IsHandleCreated);
     }
 
+    [WinFormsFact]
+    public void ProgressBar_RecreateHandle_WithAmbientBackColorInLightMode_SendsAmbientBackColor()
+    {
+        using Form parent = new()
+        {
+            BackColor = Color.OrangeRed
+        };
+        using SubProgressBar progressBar = new();
+        parent.Controls.Add(progressBar);
+
+        parent.CreateControl();
+        Assert.NotEqual(IntPtr.Zero, progressBar.Handle);
+        Assert.Equal(parent.BackColor, progressBar.BackColor);
+
+        progressBar.ResetBkColorTracking();
+        progressBar.RecreateHandle();
+
+        Assert.True(progressBar.SetBkColorMessageCount > 0);
+        Assert.Equal(ColorTranslator.ToWin32(progressBar.BackColor), progressBar.LastSetBkColorMessage);
+    }
+
+    [WinFormsFact]
+    public void ProgressBar_StyleSwitch_WithCustomBackColorInLightMode_SendsCustomBackColor()
+    {
+        using Form parent = new();
+        using SubProgressBar progressBar = new()
+        {
+            BackColor = Color.White,
+            Style = ProgressBarStyle.Blocks
+        };
+        parent.Controls.Add(progressBar);
+
+        parent.CreateControl();
+        Assert.NotEqual(IntPtr.Zero, progressBar.Handle);
+
+        progressBar.ResetColorTracking();
+        progressBar.Style = ProgressBarStyle.Continuous;
+
+        Assert.True(progressBar.SetBkColorMessageCount > 0);
+        Assert.Equal(ColorTranslator.ToWin32(progressBar.BackColor), progressBar.LastSetBkColorMessage);
+    }
+
+    [WinFormsFact]
+    public void ProgressBar_StyleSwitch_WithCustomForeColorInLightMode_SendsCustomForeColor()
+    {
+        using Form parent = new();
+        using SubProgressBar progressBar = new()
+        {
+            ForeColor = Color.LimeGreen,
+            Style = ProgressBarStyle.Blocks
+        };
+        parent.Controls.Add(progressBar);
+
+        parent.CreateControl();
+        Assert.NotEqual(IntPtr.Zero, progressBar.Handle);
+
+        progressBar.ResetColorTracking();
+        progressBar.Style = ProgressBarStyle.Continuous;
+
+        Assert.True(progressBar.SetBarColorMessageCount > 0);
+        Assert.Equal(ColorTranslator.ToWin32(progressBar.ForeColor), progressBar.LastSetBarColorMessage);
+    }
+
     [WinFormsTheory]
     [NewAndDefaultData<EventArgs>]
     public void ProgressBar_OnHandleDestroyed_Invoke_CallsHandleDestroyed(EventArgs eventArgs)
@@ -2641,6 +2704,8 @@ public class SubProgressBar : ProgressBar
 
         public new void CreateHandle() => base.CreateHandle();
 
+        public new void RecreateHandle() => base.RecreateHandle();
+
         public new AutoSizeMode GetAutoSizeMode() => base.GetAutoSizeMode();
 
         public new bool GetStyle(ControlStyles flag) => base.GetStyle(flag);
@@ -2674,5 +2739,42 @@ public class SubProgressBar : ProgressBar
         public new void OnRightToLeftLayoutChanged(EventArgs e) => base.OnRightToLeftLayoutChanged(e);
 
         public new void SetStyle(ControlStyles flag, bool value) => base.SetStyle(flag, value);
+
+        public int? LastSetBkColorMessage { get; private set; }
+
+        public int? LastSetBarColorMessage { get; private set; }
+
+        public int SetBkColorMessageCount { get; private set; }
+
+        public int SetBarColorMessageCount { get; private set; }
+
+        public void ResetColorTracking()
+        {
+            LastSetBkColorMessage = null;
+            LastSetBarColorMessage = null;
+            SetBkColorMessageCount = 0;
+            SetBarColorMessageCount = 0;
+        }
+
+        public void ResetBkColorTracking()
+        {
+            ResetColorTracking();
+        }
+
+        protected override void WndProc(ref Message m)
+        {
+            if (m.Msg == (int)PInvoke.PBM_SETBKCOLOR)
+            {
+                SetBkColorMessageCount++;
+                LastSetBkColorMessage = unchecked((int)m.LParam);
+            }
+            else if (m.Msg == (int)PInvoke.PBM_SETBARCOLOR)
+            {
+                SetBarColorMessageCount++;
+                LastSetBarColorMessage = unchecked((int)m.LParam);
+            }
+
+            base.WndProc(ref m);
+        }
     }
 }