Give the preview tab a purple snowflake instead of a blue pin

The freeze affordance was a pushpin, and the preview-tab accent stripe was the
same blue as the selection highlight -- so a selected preview tab read as just
'selected'. Swap the glyph for a snowflake (matches the Freeze verb) and the
accent to purple (#9B59B6), keeping the One visually distinct from a
blue-highlighted selected tab. The snowflake is a stroked vector Path with its
Stroke bound to the tab Foreground (theme-inherited), six spokes + tip barbs,
no rotation.

Assisted-by: Claude:claude-opus-4-8:Claude Code

ILSpy.Tests/Docking/PreviewTabPromotionTests.cs

@@ -210,6 +210,11 @@ public class PreviewTabPromotionTests
 			"the preview MainTab must carry the accent BorderBrush");
 		mainTabItem.BorderThickness.Should().Be(new global::Avalonia.Thickness(3, 0, 0, 0),
 			"the preview MainTab must carry the left-only 3px accent stripe");
+		// The accent is purple (#9B59B6) -- deliberately not the selection/toolbar blue, so the
+		// One stays distinct from a blue-highlighted selected tab.
+		(mainTabItem.BorderBrush as global::Avalonia.Media.ISolidColorBrush)!.Color
+			.Should().Be(global::Avalonia.Media.Color.FromRgb(0x9B, 0x59, 0xB6),
+				"the preview accent stripe must be purple, not blue");
 	}
 
 	[AvaloniaTest]

ILSpy/Themes/BoolToBrushConverter.cs

@@ -33,10 +33,12 @@ namespace ILSpy.Themes
 	/// </summary>
 	public sealed class BoolToBrushConverter : IValueConverter
 	{
-		/// <summary>Static accent for the preview-tab left-edge stripe — matches the
-		/// toolbar accent palette (#0078D7).</summary>
+		/// <summary>Static accent for the preview-tab left-edge stripe. Purple (#9B59B6),
+		/// deliberately NOT the selection/toolbar blue — so the One preview tab stays visually
+		/// distinct from a blue-highlighted *selected* tab even when it is itself selected. Reads
+		/// against both light and dark tab-strip backgrounds.</summary>
 		public static readonly BoolToBrushConverter PreviewAccent = new() {
-			TrueBrush = new ImmutableSolidColorBrush(Color.FromRgb(0x00, 0x78, 0xD7)),
+			TrueBrush = new ImmutableSolidColorBrush(Color.FromRgb(0x9B, 0x59, 0xB6)),
 		};
 
 		public IBrush? TrueBrush { get; init; }

ILSpy/Themes/PreviewTabFreezeButtonBehavior.cs

@@ -102,24 +102,27 @@ namespace ILSpy.Themes
 			// paint on top of it.
 			titleStack.ClipToBounds = true;
 
-			// Tilted-pushpin silhouette matching the Visual Studio preview-tab affordance.
-			// Vector path (not a font glyph): the previous Segoe Fluent Icons U+E718
-			// fallback was Windows-only and rendered as a tofu box on Linux / macOS.
-			// Path with bound Fill is what restores per-tab Foreground inheritance that
-			// the intermediate SVG-image variant lost - Avalonia.Svg.Skia honors the
-			// asset's literal fill, not the consuming control's theme color. RotateTransform
-			// at -45 deg orients the upright pin path so its tip points to the lower-left.
+			// Snowflake glyph for "freeze". A STROKED vector Path (not a font glyph): the
+			// previous Segoe Fluent fallback was Windows-only and rendered as tofu on Linux /
+			// macOS. Six spokes + tip barbs in a 16x16 box (inset so the stroke isn't clipped
+			// at the tips). Stroke (not Fill) is bound to the tab's Foreground so the glyph
+			// inherits the per-tab theme colour.
 			var glyph = new Path {
-				Data = StreamGeometry.Parse("M5 2h6v1h-1v4l2 2v1H9v3l-1 2-1-2v-3H4V9l2-2V3H5z"),
+				Data = StreamGeometry.Parse(
+					"M8,1.5 L8,14.5 M2.37,4.75 L13.63,11.25 M2.37,11.25 L13.63,4.75 " +
+					"M8,4.2 L6.6,2.9 M8,4.2 L9.4,2.9 M8,11.8 L6.6,13.1 M8,11.8 L9.4,13.1 " +
+					"M5.0,5.9 L3.4,5.5 M5.0,5.9 L4.6,7.5 M11.0,10.1 L12.6,10.5 M11.0,10.1 L11.4,8.5 " +
+					"M5.0,10.1 L3.4,10.5 M5.0,10.1 L4.6,8.5 M11.0,5.9 L12.6,5.5 M11.0,5.9 L11.4,7.5"),
 				Stretch = Stretch.Uniform,
+				StrokeThickness = 1.3,
+				StrokeLineCap = PenLineCap.Round,
+				StrokeJoin = PenLineJoin.Round,
 				Width = 12,
 				Height = 12,
 				HorizontalAlignment = HorizontalAlignment.Center,
 				VerticalAlignment = VerticalAlignment.Center,
-				RenderTransform = new RotateTransform(45),
-				RenderTransformOrigin = RelativePoint.Center,
 			};
-			glyph.Bind(Shape.FillProperty, new Binding(nameof(TemplatedControl.Foreground)) {
+			glyph.Bind(Shape.StrokeProperty, new Binding(nameof(TemplatedControl.Foreground)) {
 				Source = item,
 				Mode = BindingMode.OneWay,
 			});