Colour the update banner by state and fix dark-mode text

The banner used one amber colour for every state. Show green when ILSpy
is up to date and amber when an update is available, driven by a new
UpdatePanelViewModel.UpdateAvailable bound to a style class on the border.

The message text also inherited the dark theme's near-white foreground,
which was unreadable on the always-light banner; pin it to a dark colour
since the banner stays light in both themes.

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

ILSpy.Tests/Updates/UpdatePanelViewModelTests.cs

@@ -0,0 +1,67 @@
+// Copyright (c) 2026 AlphaSierraPapa for the SharpDevelop Team
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy of this
+// software and associated documentation files (the "Software"), to deal in the Software
+// without restriction, including without limitation the rights to use, copy, modify, merge,
+// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
+// to whom the Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all copies or
+// substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
+// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+using System.Collections.Generic;
+using System.ComponentModel;
+
+using Avalonia.Headless.NUnit;
+
+using AwesomeAssertions;
+
+using ILSpy.AppEnv;
+using ILSpy.ViewModels;
+
+using NUnit.Framework;
+
+namespace ICSharpCode.ILSpy.Tests.Updates;
+
+/// <summary>
+/// The update banner colours itself by state: green when ILSpy is up to date, amber when an
+/// update is available. <see cref="UpdatePanelViewModel.UpdateAvailable"/> is the boolean that
+/// drives that (bound to a style class in the view), so pin that it tracks the download URL.
+/// </summary>
+[TestFixture]
+public class UpdatePanelViewModelTests
+{
+	[AvaloniaTest]
+	public void UpdateAvailable_tracks_the_download_url()
+	{
+		var vm = AppComposition.Current.GetExport<UpdatePanelViewModel>();
+
+		vm.UpdateAvailableDownloadUrl = null;
+		vm.UpdateAvailable.Should().BeFalse("no download URL means ILSpy is up to date");
+
+		vm.UpdateAvailableDownloadUrl = "https://example.invalid/ILSpy.zip";
+		vm.UpdateAvailable.Should().BeTrue("a download URL means an update is available");
+	}
+
+	[AvaloniaTest]
+	public void Setting_the_download_url_notifies_UpdateAvailable()
+	{
+		var vm = AppComposition.Current.GetExport<UpdatePanelViewModel>();
+		vm.UpdateAvailableDownloadUrl = null;
+
+		var changed = new List<string?>();
+		vm.PropertyChanged += (_, e) => changed.Add(e.PropertyName);
+
+		vm.UpdateAvailableDownloadUrl = "https://example.invalid/ILSpy.zip";
+
+		changed.Should().Contain(nameof(UpdatePanelViewModel.UpdateAvailable),
+			"the banner colour binds to UpdateAvailable, so it must raise PropertyChanged for it");
+	}
+}

ILSpy/ViewModels/UpdatePanelViewModel.cs

@@ -51,6 +51,7 @@ namespace ILSpy.ViewModels
 		[ObservableProperty]
 		[NotifyPropertyChangedFor(nameof(ButtonText))]
 		[NotifyPropertyChangedFor(nameof(Message))]
+		[NotifyPropertyChangedFor(nameof(UpdateAvailable))]
 		string? updateAvailableDownloadUrl;
 
 		[ObservableProperty]
@@ -64,6 +65,10 @@ namespace ILSpy.ViewModels
 			? "A new version of ILSpy is available."
 			: "ILSpy is up to date.";
 
+		/// <summary>True once a download URL is known. Drives the banner colour: amber when an
+		/// update is available, green when ILSpy is up to date.</summary>
+		public bool UpdateAvailable => UpdateAvailableDownloadUrl != null;
+
 		[RelayCommand]
 		void Close() => IsPanelVisible = false;
 

ILSpy/Views/UpdatePanel.axaml

@@ -4,9 +4,25 @@
              x:Class="ILSpy.Views.UpdatePanel"
              x:DataType="vm:UpdatePanelViewModel"
              IsVisible="{Binding IsPanelVisible}">
-	<Border Background="#FFFFE08A" BorderBrush="#FFCC8800" BorderThickness="0,0,0,1" Padding="8,4">
+	<UserControl.Styles>
+		<!-- The banner colours itself by state: green when ILSpy is up to date (default, no
+		     class), amber when an update is available (the .updateAvailable class, toggled from
+		     UpdatePanelViewModel.UpdateAvailable). -->
+		<Style Selector="Border#PanelBorder">
+			<Setter Property="Background" Value="#FFDFF0D8" />
+			<Setter Property="BorderBrush" Value="#FF4F8A10" />
+		</Style>
+		<Style Selector="Border#PanelBorder.updateAvailable">
+			<Setter Property="Background" Value="#FFFFE08A" />
+			<Setter Property="BorderBrush" Value="#FFCC8800" />
+		</Style>
+	</UserControl.Styles>
+	<Border Name="PanelBorder" Classes.updateAvailable="{Binding UpdateAvailable}"
+	        BorderThickness="0,0,0,1" Padding="8,4">
 		<Grid ColumnDefinitions="*,Auto,Auto" ColumnSpacing="8">
-			<TextBlock Grid.Column="0" VerticalAlignment="Center" Text="{Binding Message}" />
+			<!-- Fixed dark foreground: the banner stays a light colour in both themes, so the
+			     dark theme's near-white default foreground would be unreadable on it. -->
+			<TextBlock Grid.Column="0" VerticalAlignment="Center" Foreground="Black" Text="{Binding Message}" />
 			<Button Grid.Column="1" Content="{Binding ButtonText}"
 			        Command="{Binding DownloadOrCheckUpdateCommand}" />
 			<Button Grid.Column="2" Content="&#x2715;" Width="24" Padding="0"