Fixes: Regression in ColorPicker ColorPalette

components/ColorPicker/src/ColorPicker.cs

@@ -764,6 +764,11 @@ private void UpdateColorControlValues()
                 }
             }
 
+            if (this.PaletteItemGridView != null)
+            {
+                this.PaletteItemGridView.SelectedItem = (this.CustomPaletteColors?.Contains(rgbColor) ?? false) ? rgbColor : null;
+            }
+
             if (eventsDisconnectedByMethod)
             {
                 this.ConnectEvents(true);

components/ColorPicker/tests/ColorPicker.Tests.projitems

@@ -13,6 +13,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)ExampleColorPickerTestPage.xaml.cs">
       <DependentUpon>ExampleColorPickerTestPage.xaml</DependentUpon>
     </Compile>
+    <Compile Include="$(MSBuildThisFileDirectory)PaletteSelectionTests.cs" />
   </ItemGroup>
   <ItemGroup>
     <Page Include="$(MSBuildThisFileDirectory)ExampleColorPickerTestPage.xaml">

components/ColorPicker/tests/PaletteSelectionTests.cs

@@ -0,0 +1,73 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using CommunityToolkit.Tooling.TestGen;
+using CommunityToolkit.Tests;
+using CommunityToolkit.WinUI.Controls;
+using Microsoft.UI.Xaml.Controls;
+using ColorPicker = CommunityToolkit.WinUI.Controls.ColorPicker;
+
+namespace ColorPickerTests;
+
+[TestClass]
+public partial class PaletteSelectionTests : VisualUITestBase
+{
+    // First color in FluentColorPalette (#ffb900)
+    private static readonly Windows.UI.Color PaletteColor = Windows.UI.Color.FromArgb(255, 255, 185, 0);
+
+    // Second palette color for the round-trip check (#d13438)
+    private static readonly Windows.UI.Color PaletteColor2 = Windows.UI.Color.FromArgb(255, 209, 52, 56);
+
+    // White is not in the FluentColorPalette
+    private static readonly Windows.UI.Color NonPaletteColor = Colors.White;
+
+    /// <summary>
+    /// Verifies that the palette GridView selection follows the Color property when it is changed
+    /// programmatically (e.g. via the spectrum or sliders). Regression test for issue #833.
+    /// </summary>
+    [UIThreadTestMethod]
+    public async Task PaletteGridView_FollowsColorProperty()
+    {
+        var colorPicker = new ColorPicker();
+        await LoadTestContentAsync(colorPicker);
+        await CompositionTargetHelper.ExecuteAfterCompositionRenderingAsync(() => { });
+
+        // The PaletteItemGridView lives inside a SwitchPresenter Case that is only added to
+        // the visual tree once the palette tab is selected. Navigate there first.
+        var panelSelector = colorPicker.FindDescendant<Segmented>();
+        Assert.IsNotNull(panelSelector, "Could not find ColorPanelSelector in visual tree.");
+
+        var paletteItem = panelSelector.FindDescendant("PaletteItem") as SegmentedItem;
+        Assert.IsNotNull(paletteItem, "Could not find PaletteItem in ColorPanelSelector.");
+
+        panelSelector.SelectedItem = paletteItem;
+        await CompositionTargetHelper.ExecuteAfterCompositionRenderingAsync(() => { });
+
+        var paletteGridView = colorPicker.FindDescendant("PaletteItemGridView") as GridView;
+        Assert.IsNotNull(paletteGridView, "Could not find PaletteItemGridView in visual tree.");
+
+        // Set to a color that is in the default palette — selection should follow.
+        colorPicker.Color = PaletteColor;
+        await CompositionTargetHelper.ExecuteAfterCompositionRenderingAsync(() => { });
+
+        Assert.AreEqual(PaletteColor, paletteGridView.SelectedItem,
+            "PaletteItemGridView should select the matching palette color when Color is set.");
+
+        // Set to a color not in the palette — selection should be cleared.
+        colorPicker.Color = NonPaletteColor;
+        await CompositionTargetHelper.ExecuteAfterCompositionRenderingAsync(() => { });
+
+        Assert.IsNull(paletteGridView.SelectedItem,
+            "PaletteItemGridView should have no selection when Color is not in the palette.");
+
+        // Set to a different palette color — selection should update to match.
+        colorPicker.Color = PaletteColor2;
+        await CompositionTargetHelper.ExecuteAfterCompositionRenderingAsync(() => { });
+
+        Assert.AreEqual(PaletteColor2, paletteGridView.SelectedItem,
+            "PaletteItemGridView should update its selection when Color changes to another palette color.");
+
+        await UnloadTestContentAsync(colorPicker);
+    }
+}