Add RGB hex color preview to Advanced Paste clipboard history (#43990)

<!-- Enter a brief description/summary of your PR here. What does it
fix/what does it change/how was it tested (even manually, if necessary)?
-->
## Summary of the Pull Request

This pull request adds support for recognizing and displaying clipboard
items that are valid RGB hex color codes (such as `#FFBFAB` or `#abc`)
in the Advanced Paste module. It introduces logic to detect hex color
strings, converts them to color values, and updates the UI to show a
color preview for these items. The changes also include comprehensive
unit tests for the new functionality.

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## PR Checklist

- [x] Closes: #43538
<!-- - [ ] Closes: #yyy (add separate lines for additional resolved
issues) -->
- [x] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [x] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
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pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
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- [ ] **Documentation updated:** If checked, please file a pull request
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and link it here: #xxx

<!-- Provide a more detailed description of the PR, other things fixed,
or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

**Clipboard color detection and conversion:**

* Added `ClipboardItemHelper.IsRgbHexColor` method using a compiled
regex to identify valid hex color strings in clipboard text.
[[1]](diffhunk://#diff-7429196ad30cd0bce57b102669da4dc13d43a09579e99ceac7cc0f7dc101cd2bR62-R86)
[[2]](diffhunk://#diff-7429196ad30cd0bce57b102669da4dc13d43a09579e99ceac7cc0f7dc101cd2bR112-R114)
* Introduced `HexColorConverterHelper.ConvertHexColorToRgb` utility to
convert hex color strings to `Windows.UI.Color`, handling both 3-digit
and 6-digit formats.

**UI enhancements for color previews:**

* Updated `ClipboardHistoryItemPreviewControl` to include a color
preview grid that displays an ellipse filled with the detected color and
the color code as text, using the new `HexColorToBrushConverter`.
[[1]](diffhunk://#diff-2ed6014d4c17037b9cd0ab397e40b9069b1e7fe47a700673f34e8217d78124d5R29-R48)
[[2]](diffhunk://#diff-2ed6014d4c17037b9cd0ab397e40b9069b1e7fe47a700673f34e8217d78124d5R14)
[[3]](diffhunk://#diff-0c26c92697f6bb38fa40160fc8b18f0876ddc8d828a510034411001aa2e05063R1-R28)
* Modified logic in `ClipboardHistoryItemPreviewControl.xaml.cs` to
ensure color previews are shown only for detected color items and to
adjust visibility of text and glyph previews accordingly.

**Unit tests for color detection and conversion:**

* Added unit tests for hex color conversion
(`HexColorToColorConverterTests.cs`) and color detection logic
(`ClipboardItemHelperTests.cs`) to verify correct behavior for valid,
invalid, and edge-case inputs.
[[1]](diffhunk://#diff-d81d997d5fb414f1563c31c38681113aaa9c847ef05bb77662d30bd1310d6b8eR1-R61)
[[2]](diffhunk://#diff-185e8954ca6f061bf5d60d0c61ac6cfd87bd1a48ebda11a8172e3496a050fe85R1-R36)

<!-- Describe how you validated the behavior. Add automated tests
wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed
* Copied to the clipboard a color encoded text like: #FFBFAB
* Opened Advanced Paste and noticed the color: 

<img width="467" height="309" alt="image"
src="https://github.com/user-attachments/assets/6cedce89-9833-4efb-abf9-3cfe8e8f32f0"
/>

---------

Co-authored-by: Copilot <198982749+Copilot@users.noreply.github.com>
Co-authored-by: crramirez <8397379+crramirez@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

src/modules/AdvancedPaste/AdvancedPaste.UnitTests/ConvertersTests/HexColorToColorConverterTests.cs

@@ -0,0 +1,56 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using AdvancedPaste.Converters;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Windows.UI;
+
+namespace AdvancedPaste.UnitTests.ConvertersTests;
+
+[TestClass]
+public sealed class HexColorToColorConverterTests
+{
+    [TestMethod]
+    public void TestConvert_ValidSixDigitHex_ReturnsColor()
+    {
+        Color? result = HexColorConverterHelper.ConvertHexColorToRgb("#FFBFAB");
+        Assert.IsNotNull(result);
+
+        var color = (Windows.UI.Color)result;
+        Assert.AreEqual(255, color.R);
+        Assert.AreEqual(191, color.G);
+        Assert.AreEqual(171, color.B);
+        Assert.AreEqual(255, color.A);
+    }
+
+    [TestMethod]
+    public void TestConvert_ValidThreeDigitHex_ReturnsColor()
+    {
+        Color? result = HexColorConverterHelper.ConvertHexColorToRgb("#abc");
+        Assert.IsNotNull(result);
+
+        var color = (Windows.UI.Color)result;
+
+        // #abc should expand to #aabbcc
+        Assert.AreEqual(170, color.R); // 0xaa
+        Assert.AreEqual(187, color.G); // 0xbb
+        Assert.AreEqual(204, color.B); // 0xcc
+        Assert.AreEqual(255, color.A);
+    }
+
+    [TestMethod]
+    public void TestConvert_NullOrEmpty_ReturnsNull()
+    {
+        Assert.IsNull(HexColorConverterHelper.ConvertHexColorToRgb(null));
+        Assert.IsNull(HexColorConverterHelper.ConvertHexColorToRgb(string.Empty));
+        Assert.IsNull(HexColorConverterHelper.ConvertHexColorToRgb("   "));
+    }
+
+    [TestMethod]
+    public void TestConvert_InvalidHex_ReturnsNull()
+    {
+        Assert.IsNull(HexColorConverterHelper.ConvertHexColorToRgb("#GGGGGG"));
+        Assert.IsNull(HexColorConverterHelper.ConvertHexColorToRgb("#12345"));
+    }
+}

src/modules/AdvancedPaste/AdvancedPaste.UnitTests/HelpersTests/ClipboardItemHelperTests.cs

@@ -0,0 +1,36 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using AdvancedPaste.Helpers;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace AdvancedPaste.UnitTests.HelpersTests;
+
+[TestClass]
+public sealed class ClipboardItemHelperTests
+{
+    [TestMethod]
+    [DataRow("#FFBFAB", true)]
+    [DataRow("#000000", true)]
+    [DataRow("#FFFFFF", true)]
+    [DataRow("#fff", true)]
+    [DataRow("#abc", true)]
+    [DataRow("#123456", true)]
+    [DataRow("#AbCdEf", true)]
+    [DataRow("FFBFAB", false)] // Missing #
+    [DataRow("#GGGGGG", false)] // Invalid hex characters
+    [DataRow("#12345", false)] // Wrong length
+    [DataRow("#1234567", false)] // Too long
+    [DataRow("", false)]
+    [DataRow(null, false)]
+    [DataRow("  #FFF  ", true)] // Whitespace should be trimmed
+    [DataRow("Not a color", false)]
+    [DataRow("#", false)]
+    [DataRow("##FFFFFF", false)]
+    public void TestIsRgbHexColor(string input, bool expected)
+    {
+        bool result = ClipboardItemHelper.IsRgbHexColor(input);
+        Assert.AreEqual(expected, result, $"IsRgbHexColor(\"{input}\") should return {expected}");
+    }
+}

src/modules/AdvancedPaste/AdvancedPaste/AdvancedPasteXAML/Controls/ClipboardHistoryItemPreviewControl.xaml

@@ -11,6 +11,7 @@
     mc:Ignorable="d">
     <UserControl.Resources>
         <converters:DateTimeToFriendlyStringConverter x:Key="DateTimeToFriendlyStringConverter" />
+        <converters:HexColorToBrushConverter x:Key="HexColorToBrushConverter" />
         <tkconverters:BoolToVisibilityConverter x:Name="BoolToVisibilityConverter" />
     </UserControl.Resources>
     <Grid ColumnSpacing="12">
@@ -25,6 +26,26 @@
                     Source="{x:Bind ClipboardItem.Image, Mode=OneWay}"
                     Stretch="UniformToFill"
                     Visibility="{x:Bind HasImage, Mode=OneWay, Converter={StaticResource BoolToVisibilityConverter}}" />
+                <!--  Color preview with text  -->
+                <Grid Visibility="{x:Bind HasColor, Mode=OneWay, Converter={StaticResource BoolToVisibilityConverter}}">
+                    <Grid.ColumnDefinitions>
+                        <ColumnDefinition Width="Auto" />
+                        <ColumnDefinition Width="*" />
+                    </Grid.ColumnDefinitions>
+                    <Ellipse
+                        Grid.Column="0"
+                        Width="8"
+                        Height="8"
+                        Margin="8,0,8,0"
+                        Fill="{x:Bind ClipboardItem.Content, Mode=OneWay, Converter={StaticResource HexColorToBrushConverter}}" />
+                    <TextBlock
+                        Grid.Column="1"
+                        VerticalAlignment="Center"
+                        FontSize="10"
+                        Foreground="{ThemeResource TextFillColorSecondaryBrush}"
+                        Text="{x:Bind ClipboardItem.Content, Mode=OneWay}"
+                        TextWrapping="NoWrap" />
+                </Grid>
                 <!--  Text preview  -->
                 <TextBlock
                     Margin="8,0,0,0"

src/modules/AdvancedPaste/AdvancedPaste/AdvancedPasteXAML/Controls/ClipboardHistoryItemPreviewControl.xaml.cs

@@ -38,9 +38,11 @@ namespace AdvancedPaste.Controls
 
         public bool HasImage => ContentImage is not null;
 
-        public bool HasText => !string.IsNullOrEmpty(ContentText) && !HasImage;
+        public bool HasText => !string.IsNullOrEmpty(ContentText) && !HasImage && !HasColor;
 
-        public bool HasGlyph => !HasImage && !HasText && !string.IsNullOrEmpty(IconGlyph);
+        public bool HasGlyph => !HasImage && !HasText && !HasColor && !string.IsNullOrEmpty(IconGlyph);
+
+        public bool HasColor => ClipboardItemHelper.IsRgbHexColor(ContentText);
 
         public ClipboardHistoryItemPreviewControl()
         {

src/modules/AdvancedPaste/AdvancedPaste/AdvancedPasteXAML/Converters/HexColorConverterHelper.cs

@@ -0,0 +1,39 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace AdvancedPaste.Converters
+{
+    public static class HexColorConverterHelper
+    {
+        public static Windows.UI.Color? ConvertHexColorToRgb(string hexColor)
+        {
+            try
+            {
+                // Remove # if present
+                var cleanHex = hexColor.TrimStart('#');
+
+                // Expand 3-digit hex to 6-digit (#ABC -> #AABBCC)
+                if (cleanHex.Length == 3)
+                {
+                    cleanHex = $"{cleanHex[0]}{cleanHex[0]}{cleanHex[1]}{cleanHex[1]}{cleanHex[2]}{cleanHex[2]}";
+                }
+
+                if (cleanHex.Length == 6)
+                {
+                    var r = System.Convert.ToByte(cleanHex.Substring(0, 2), 16);
+                    var g = System.Convert.ToByte(cleanHex.Substring(2, 2), 16);
+                    var b = System.Convert.ToByte(cleanHex.Substring(4, 2), 16);
+
+                    return Windows.UI.Color.FromArgb(255, r, g, b);
+                }
+            }
+            catch
+            {
+                // Invalid color format - return null
+            }
+
+            return null;
+        }
+    }
+}

src/modules/AdvancedPaste/AdvancedPaste/AdvancedPasteXAML/Converters/HexColorToBrushConverter.cs

@@ -0,0 +1,28 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using Microsoft.UI.Xaml.Data;
+using Microsoft.UI.Xaml.Media;
+
+namespace AdvancedPaste.Converters
+{
+    public sealed partial class HexColorToBrushConverter : IValueConverter
+    {
+        public object ConvertBack(object value, Type targetType, object parameter, string language)
+            => throw new NotSupportedException();
+
+        public object Convert(object value, Type targetType, object parameter, string language)
+        {
+            if (value is not string hexColor || string.IsNullOrWhiteSpace(hexColor))
+            {
+                return null;
+            }
+
+            Windows.UI.Color? color = HexColorConverterHelper.ConvertHexColorToRgb(hexColor);
+
+            return color != null ? new SolidColorBrush((Windows.UI.Color)color) : null;
+        }
+    }
+}

src/modules/AdvancedPaste/AdvancedPaste/Helpers/ClipboardItemHelper.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Text.RegularExpressions;
 using System.Threading.Tasks;
 using AdvancedPaste.Models;
 using Microsoft.UI.Xaml.Media.Imaging;
@@ -10,8 +11,11 @@ using Windows.ApplicationModel.DataTransfer;
 
 namespace AdvancedPaste.Helpers
 {
-    internal static class ClipboardItemHelper
+    internal static partial class ClipboardItemHelper
     {
+        // Compiled regex for better performance when checking multiple clipboard items
+        private static readonly Regex HexColorRegex = HexColorCompiledRegex();
+
         /// <summary>
         /// Creates a ClipboardItem from current clipboard data.
         /// </summary>
@@ -55,6 +59,31 @@ namespace AdvancedPaste.Helpers
             return clipboardItem;
         }
 
+        /// <summary>
+        /// Checks if text is a valid RGB hex color (e.g., #FFBFAB or #fff).
+        /// </summary>
+        public static bool IsRgbHexColor(string text)
+        {
+            if (text == null)
+            {
+                return false;
+            }
+
+            string trimmedText = text.Trim();
+            if (trimmedText.Length > 7)
+            {
+                return false;
+            }
+
+            if (string.IsNullOrWhiteSpace(trimmedText))
+            {
+                return false;
+            }
+
+            // Match #RGB or #RRGGBB format (case-insensitive)
+            return HexColorRegex.IsMatch(trimmedText);
+        }
+
         /// <summary>
         /// Creates a BitmapImage from clipboard data.
         /// </summary>
@@ -80,5 +109,8 @@ namespace AdvancedPaste.Helpers
 
             return null;
         }
+
+        [GeneratedRegex(@"^#([0-9A-Fa-f]{3}|[0-9A-Fa-f]{6})$")]
+        private static partial Regex HexColorCompiledRegex();
     }
 }