Enable DataGridView dark mode theming via AppContext switch

src/System.Windows.Forms.Primitives/src/System/LocalAppContextSwitches/LocalAppContextSwitches.cs

@@ -26,6 +26,7 @@ internal static partial class LocalAppContextSwitches
     internal const string EnableMsoComponentManagerSwitchName = "Switch.System.Windows.Forms.EnableMsoComponentManager";
     internal const string TreeNodeCollectionAddRangeRespectsSortOrderSwitchName = "System.Windows.Forms.TreeNodeCollectionAddRangeRespectsSortOrder";
     internal const string MoveTreeViewTextLocationOnePixelSwitchName = "System.Windows.Forms.TreeView.MoveTreeViewTextLocationOnePixel";
+    internal const string DataGridViewDarkModeThemingSwitchName = "System.Windows.Forms.DataGridViewDarkModeTheming";
 
     private static int s_scaleTopLevelFormMinMaxSizeForDpi;
     private static int s_anchorLayoutV2;
@@ -39,6 +40,7 @@ internal static partial class LocalAppContextSwitches
     private static int s_treeNodeCollectionAddRangeRespectsSortOrder;
 
     private static int s_moveTreeViewTextLocationOnePixel;
+    private static int s_dataGridViewDarkModeTheming;
 
     private static FrameworkName? s_targetFrameworkName;
 
@@ -134,6 +136,16 @@ private static bool GetSwitchDefaultValue(string switchName)
             }
         }
 
+        if (framework.Version.Major >= 10)
+        {
+            // Behavior changes added in .NET 10
+
+            if (switchName == DataGridViewDarkModeThemingSwitchName)
+            {
+                return true;
+            }
+        }
+
         return false;
     }
 
@@ -231,4 +243,15 @@ public static bool MoveTreeViewTextLocationOnePixel
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         get => GetCachedSwitchValue(MoveTreeViewTextLocationOnePixelSwitchName, ref s_moveTreeViewTextLocationOnePixel);
     }
+
+    /// <summary>
+    ///  Indicates whether dark mode theming is automatically applied to DataGridView
+    ///  controls when the application is running in dark mode. Defaults to <see langword="true"/>
+    ///  for .NET 10+ applications. Set to <see langword="false"/> to opt out.
+    /// </summary>
+    public static bool DataGridViewDarkModeTheming
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get => GetCachedSwitchValue(DataGridViewDarkModeThemingSwitchName, ref s_dataGridViewDarkModeTheming);
+    }
 }

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

@@ -3,6 +3,8 @@ static System.Windows.Forms.TaskDialog.ShowDialogAsync(nint hwndOwner, System.Wi
 static System.Windows.Forms.TaskDialog.ShowDialogAsync(System.Windows.Forms.IWin32Window! owner, System.Windows.Forms.TaskDialogPage! page, System.Windows.Forms.TaskDialogStartupLocation startupLocation = System.Windows.Forms.TaskDialogStartupLocation.CenterOwner) -> System.Threading.Tasks.Task<System.Windows.Forms.TaskDialogButton!>!
 static System.Windows.Forms.TaskDialog.ShowDialogAsync(System.Windows.Forms.TaskDialogPage! page, System.Windows.Forms.TaskDialogStartupLocation startupLocation = System.Windows.Forms.TaskDialogStartupLocation.CenterScreen) -> System.Threading.Tasks.Task<System.Windows.Forms.TaskDialogButton!>!
 System.Windows.Forms.ControlStyles.ApplyThemingImplicitly = 524288 -> System.Windows.Forms.ControlStyles
+System.Windows.Forms.DataGridViewCellStyle.SortGlyphColor.get -> System.Drawing.Color
+System.Windows.Forms.DataGridViewCellStyle.SortGlyphColor.set -> void
 System.Windows.Forms.Form.FormBorderColorChanged -> System.EventHandler?
 System.Windows.Forms.Form.FormCaptionBackColorChanged -> System.EventHandler?
 System.Windows.Forms.Form.FormCaptionTextColorChanged -> System.EventHandler?

src/System.Windows.Forms/System/Windows/Forms/Controls/DataGridView/DataGridView.Methods.cs

@@ -17,6 +17,51 @@ namespace System.Windows.Forms;
 
 public partial class DataGridView
 {
+    // A medium accent blue commonly used for selection highlights in dark UI.
+    private static readonly Color s_darkModeSelectionBackground = Color.FromArgb(0x33, 0x66, 0xCC);
+
+    /// <summary>
+    ///  Applies dark mode theming to the DataGridView when the application is running
+    ///  in dark mode. This is called automatically from <see cref="OnHandleCreated"/>
+    ///  when the <c>System.Windows.Forms.DataGridViewDarkModeTheming</c> AppContext switch
+    ///  is enabled (default for .NET 10+).
+    /// </summary>
+    private void ApplyDarkModeTheming()
+    {
+        Color surface = SystemColors.Window;
+        Color onSurface = SystemColors.WindowText;
+        Color headerBg = SystemColors.ControlDarkDark;
+        Color headerFg = SystemColors.ActiveCaptionText;
+        Color selectionBg = s_darkModeSelectionBackground;
+        Color selectionFg = Color.White;
+
+        // Disable the header's system theme so that our custom styles are not overridden by the system.
+        EnableHeadersVisualStyles = false;
+
+        // Table body
+        BackgroundColor = surface;
+        DefaultCellStyle.BackColor = surface;
+        DefaultCellStyle.ForeColor = onSurface;
+
+        // Column headers
+        ColumnHeadersDefaultCellStyle.BackColor = headerBg;
+        ColumnHeadersDefaultCellStyle.ForeColor = headerFg;
+
+        // Light-colored dividing line
+        GridColor = ControlPaint.Light(surface, 0.50f);
+
+        // Row headers
+        RowHeadersDefaultCellStyle.BackColor = headerBg;
+        RowHeadersDefaultCellStyle.ForeColor = headerFg;
+
+        // Selected state - use Color.Empty so header selection follows body selection
+        RowHeadersDefaultCellStyle.SelectionBackColor = Color.Empty;
+        ColumnHeadersDefaultCellStyle.SelectionBackColor = Color.Empty;
+
+        DefaultCellStyle.SelectionBackColor = selectionBg;
+        DefaultCellStyle.SelectionForeColor = selectionFg;
+    }
+
     protected virtual void AccessibilityNotifyCurrentCellChanged(Point cellAddress)
     {
         if (cellAddress.X < 0 || cellAddress.X >= Columns.Count)
@@ -2853,6 +2898,20 @@ private void BuildInheritedColumnHeaderCellStyle(DataGridViewCellStyle inherited
             inheritedCellStyle.SelectionForeColor = dataGridViewStyle.SelectionForeColor;
         }
 
+        // Inherit SortGlyphColor for column header sort arrow
+        if (cellStyle is not null && !cellStyle.SortGlyphColor.IsEmpty)
+        {
+            inheritedCellStyle.SortGlyphColor = cellStyle.SortGlyphColor;
+        }
+        else if (!columnHeadersStyle.SortGlyphColor.IsEmpty)
+        {
+            inheritedCellStyle.SortGlyphColor = columnHeadersStyle.SortGlyphColor;
+        }
+        else if (!dataGridViewStyle.SortGlyphColor.IsEmpty)
+        {
+            inheritedCellStyle.SortGlyphColor = dataGridViewStyle.SortGlyphColor;
+        }
+
         inheritedCellStyle.Font = cellStyle?.Font ?? columnHeadersStyle.Font ?? dataGridViewStyle.Font;
 
         if (cellStyle is not null && !cellStyle.IsNullValueDefault)
@@ -15242,6 +15301,12 @@ protected override void OnHandleCreated(EventArgs e)
             OnGlobalAutoSize();
         }
 
+        // Automatically apply dark mode theming when enabled via quirk switch.
+        if (Application.IsDarkModeEnabled && AppContextSwitches.DataGridViewDarkModeTheming)
+        {
+            ApplyDarkModeTheming();
+        }
+
         SystemEvents.UserPreferenceChanged += OnUserPreferenceChanged;
     }
 

src/System.Windows.Forms/System/Windows/Forms/Controls/DataGridView/DataGridViewCell.cs

@@ -1435,6 +1435,18 @@ private static Bitmap GetBitmap(string bitmapName) =>
                 ? ControlPaint.LightLight(baseline)
                 : SystemColors.ControlLightLight;
         }
+        else if (Application.IsDarkModeEnabled && AppContextSwitches.DataGridViewDarkModeTheming)
+        {
+            // In Dark Mode, use higher contrast colors for better visibility.
+            // For dark backgrounds, we need lighter colors that stand out.
+            darkColor = darkDistance < ContrastThreshold
+                ? ControlPaint.Light(baseline, 0.5f)
+                : SystemColors.ControlLight;
+
+            lightColor = lightDistance < ContrastThreshold
+                ? ControlPaint.LightLight(baseline)
+                : SystemColors.ControlLightLight;
+        }
         else
         {
             darkColor = darkDistance < ContrastThreshold

src/System.Windows.Forms/System/Windows/Forms/Controls/DataGridView/DataGridViewCellStyle.cs

@@ -23,6 +23,7 @@ public class DataGridViewCellStyle : ICloneable
     private static readonly int s_propPadding = PropertyStore.CreateKey();
     private static readonly int s_propSelectionBackColor = PropertyStore.CreateKey();
     private static readonly int s_propSelectionForeColor = PropertyStore.CreateKey();
+    private static readonly int s_propSortGlyphColor = PropertyStore.CreateKey();
     private static readonly int s_propTag = PropertyStore.CreateKey();
     private static readonly int s_propWrapMode = PropertyStore.CreateKey();
     private DataGridView? _dataGridView;
@@ -59,6 +60,7 @@ public DataGridViewCellStyle(DataGridViewCellStyle dataGridViewCellStyle)
         WrapModeInternal = dataGridViewCellStyle.WrapMode;
         Tag = dataGridViewCellStyle.Tag;
         PaddingInternal = dataGridViewCellStyle.Padding;
+        SortGlyphColor = dataGridViewCellStyle.SortGlyphColor;
     }
 
     [SRDescription(nameof(SR.DataGridViewCellStyleAlignmentDescr))]
@@ -331,6 +333,25 @@ public Color SelectionForeColor
         }
     }
 
+    /// <summary>
+    ///  Gets or sets the color used to draw the sort glyph (arrow) in column headers.
+    ///  When set to <see cref="Color.Empty"/>, the glyph color is automatically
+    ///  calculated based on the background color for optimal contrast.
+    /// </summary>
+    [SRCategory(nameof(SR.CatAppearance))]
+    public Color SortGlyphColor
+    {
+        get => Properties.GetValueOrDefault<Color>(s_propSortGlyphColor);
+        set
+        {
+            Color previous = Properties.AddOrRemoveValue(s_propSortGlyphColor, value);
+            if (!previous.Equals(value))
+            {
+                OnPropertyChanged(DataGridViewCellStylePropertyInternal.Color);
+            }
+        }
+    }
+
     [Browsable(false)]
     [DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
     public object? Tag
@@ -439,6 +460,11 @@ public virtual void ApplyStyle(DataGridViewCellStyle dataGridViewCellStyle)
         {
             PaddingInternal = dataGridViewCellStyle.Padding;
         }
+
+        if (!dataGridViewCellStyle.SortGlyphColor.IsEmpty)
+        {
+            SortGlyphColor = dataGridViewCellStyle.SortGlyphColor;
+        }
     }
 
     public virtual DataGridViewCellStyle Clone() => new(this);
@@ -465,7 +491,8 @@ internal DataGridViewCellStyleDifferences GetDifferencesFrom(DataGridViewCellSty
                 dgvcs.BackColor != BackColor ||
                 dgvcs.ForeColor != ForeColor ||
                 dgvcs.SelectionBackColor != SelectionBackColor ||
-                dgvcs.SelectionForeColor != SelectionForeColor);
+                dgvcs.SelectionForeColor != SelectionForeColor ||
+                dgvcs.SortGlyphColor != SortGlyphColor);
 
         if (preferredSizeAffectingPropDifferent)
         {
@@ -492,6 +519,7 @@ public override int GetHashCode()
         hash.Add(ForeColor);
         hash.Add(SelectionBackColor);
         hash.Add(SelectionForeColor);
+        hash.Add(SortGlyphColor);
         hash.Add(Font);
         hash.Add(NullValue);
         hash.Add(DataSourceNullValue);
@@ -530,6 +558,8 @@ internal void RemoveScope(DataGridViewCellStyleScopes scope)
 
     private bool ShouldSerializeSelectionForeColor() => Properties.ContainsKey(s_propSelectionForeColor);
 
+    private bool ShouldSerializeSortGlyphColor() => Properties.ContainsKey(s_propSortGlyphColor);
+
     public override string ToString()
     {
         StringBuilder sb = new(128);

src/System.Windows.Forms/System/Windows/Forms/Controls/DataGridView/DataGridViewCheckBoxCell.cs

@@ -1240,10 +1240,11 @@ private Rectangle PaintPrivate(
             {
                 if (paint && PaintContentForeground(paintParts))
                 {
-                    DataGridViewCheckBoxCellRenderer.DrawCheckBox(
+                    CheckBoxRenderer.DrawCheckBoxWithVisualStyles(
                         g,
-                        new Rectangle(checkBoxX, checkBoxY, checkBoxSize.Width, checkBoxSize.Height),
-                        (int)themeCheckBoxState);
+                        new Point(checkBoxX, checkBoxY),
+                        themeCheckBoxState,
+                        DataGridView.HWNDInternal);
                 }
 
                 resultBounds = new Rectangle(checkBoxX, checkBoxY, checkBoxSize.Width, checkBoxSize.Height);