Two themes, and one place that decides what colour a station is

Colours came from static brushes scattered over the windows. They now come
from a Theme, and everything that paints a station, a spot or a log row
asks Themes.Current as it paints, so changing the theme changes every
window without reopening it.

light is N1MM's own palette, read out of ApplicationStyles: the pale blue
behind a window, ivory on a button, white boxes, and the four colours a
station is painted in. dark is the same states in colours for a dark
screen, which is roughly what the program looked like before.

Config > Manage Skins, Colors and Fonts picks one, under N1MM's name for
the same dialog, and shows what each theme paints a callsign. The choice
is kept in settings.json as Theme, and light is the default.

The window chrome follows through resources the Fluent controls read, so a
text box and a button take the theme's colours in every state. Fonts and
skins are not part of it.

Looked at under Xvfb in both themes: the entry window, the theme dialog,
and the log window with its rows still coloured by what each contact was
worth.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/Nonemm.App/App.axaml.cs

@@ -1,7 +1,9 @@
 using Avalonia;
 using Avalonia.Controls.ApplicationLifetimes;
 using Avalonia.Markup.Xaml;
+using Avalonia.Media;
 using Nonemm.App.Configuration;
+using Nonemm.App.Theming;
 using Nonemm.App.Windows;
 
 namespace Nonemm.App;
@@ -16,10 +18,62 @@ public partial class App : Application
         {
             UserPaths paths = UserPaths.Default();
             paths.CreateFolders();
-            AppSession session = new(paths, Settings.Load(paths.SettingsFile));
+            Settings settings = Settings.Load(paths.SettingsFile);
+            Themes.Use(settings.Theme);
+            Themes.Changed += (_, _) => ApplyTheme();
+            ApplyTheme();
+            AppSession session = new(paths, settings);
             desktop.MainWindow = new EntryWindow(session);
             desktop.ShutdownRequested += (_, _) => session.Dispose();
         }
         base.OnFrameworkInitializationCompleted();
     }
+
+    /// The window chrome follows the theme through these resources; everything
+    /// that draws a station or a spot asks `Themes.Current` as it paints.
+    private void ApplyTheme()
+    {
+        Theme theme = Themes.Current;
+        RequestedThemeVariant = theme.Variant;
+        Set("FormBackground", theme.FormBackground);
+        Set("FormForeground", theme.FormForeground);
+        Set("FieldBackground", theme.FieldBackground);
+        Set("FieldForeground", theme.FieldForeground);
+        // the keys the Fluent controls read, so a text box and a button take
+        // the theme's colours in every state rather than only where a style of
+        // ours reaches them
+        foreach (string key in new[]
+        {
+            "TextControlBackground", "TextControlBackgroundPointerOver",
+            "TextControlBackgroundFocused", "TextControlBackgroundDisabled",
+            "ComboBoxBackground", "ComboBoxBackgroundPointerOver", "ComboBoxBackgroundPressed",
+            "DataGridRowBackgroundBrush",
+        })
+        {
+            Set(key, theme.FieldBackground);
+        }
+        foreach (string key in new[]
+        {
+            "TextControlForeground", "TextControlForegroundPointerOver",
+            "TextControlForegroundFocused", "ComboBoxForeground", "ButtonForeground",
+            "ButtonForegroundPointerOver", "ButtonForegroundPressed",
+        })
+        {
+            Set(key, theme.FieldForeground);
+        }
+        Set("ButtonBackground", theme.ButtonBackground);
+        Set("ButtonBackgroundPointerOver", Lighter(theme.ButtonBackground));
+        Set("ButtonBackgroundPressed", Darker(theme.ButtonBackground));
+    }
+
+    private void Set(string key, Color colour) => Resources[key] = new SolidColorBrush(colour);
+
+    private static Color Lighter(Color colour) => Shifted(colour, 12);
+
+    private static Color Darker(Color colour) => Shifted(colour, -18);
+
+    private static Color Shifted(Color colour, int by) => Color.FromRgb(
+        (byte)Math.Clamp(colour.R + by, 0, 255),
+        (byte)Math.Clamp(colour.G + by, 0, 255),
+        (byte)Math.Clamp(colour.B + by, 0, 255));
 }