Add Terminal theme that inherits the terminal's ANSI colour scheme

App/MainWindow.cs

@@ -415,15 +415,15 @@ private void OnThemeChanged(AppTheme theme)
 
     private string GetThemeToggleTitle()
     {
-        // Show what clicking will do: "Switch to Light" when in Dark, "Switch to Dark" when in Light
-        var currentIndex = ThemeManager.GetCurrentThemeIndex();
-        return currentIndex == 0 ? "Switch to _Light" : "Switch to _Dark";
+        // Show what clicking will do: cycle Dark -> Light -> Terminal -> Dark
+        var themes = ThemeManager.AvailableThemes;
+        var nextIndex = (ThemeManager.GetCurrentThemeIndex() + 1) % themes.Count;
+        return $"Switch to _{themes[nextIndex].Name}";
     }
 
     private void ToggleTheme()
     {
-        var currentIndex = ThemeManager.GetCurrentThemeIndex();
-        var newIndex = (currentIndex + 1) % 2;
+        var newIndex = (ThemeManager.GetCurrentThemeIndex() + 1) % ThemeManager.AvailableThemes.Count;
         ThemeManager.SetThemeByIndex(newIndex);
     }
 

App/Themes/AppTheme.cs

@@ -14,6 +14,14 @@ public abstract class AppTheme
     public abstract string Name { get; }
     public abstract string Description { get; }
 
+    /// <summary>
+    /// When true, the application restricts output to the 16 ANSI colors
+    /// (via <see cref="Application.Force16Colors"/>) so the terminal renders
+    /// the theme using its own configured ANSI palette. Themes setting this
+    /// should define all colors using <see cref="ColorName16"/> values.
+    /// </summary>
+    public virtual bool UseTerminalColors => false;
+
     // === Base Colors ===
     public abstract Color Background { get; }
     public abstract Color Foreground { get; }

App/Themes/TerminalTheme.cs

@@ -0,0 +1,105 @@
+using Terminal.Gui;
+using Attribute = Terminal.Gui.Attribute;
+
+namespace Opcilloscope.App.Themes;
+
+/// <summary>
+/// Theme that inherits the terminal's own ANSI color palette.
+/// Uses only the 16 named ANSI colors and enables Force16Colors so the
+/// driver emits standard SGR color codes (30-37/90-97) instead of 24-bit
+/// RGB - the terminal then renders them with its configured color scheme.
+/// </summary>
+public class TerminalTheme : AppTheme
+{
+    public override string Name => "Terminal";
+    public override string Description => "Inherits the terminal's ANSI color palette";
+
+    // Output only the 16 ANSI colors so the terminal applies its own palette
+    public override bool UseTerminalColors => true;
+
+    // Main window uses double-line for emphasis, frames use single
+    public override LineStyle BorderLineStyle => LineStyle.Double;
+    public override LineStyle FrameLineStyle => LineStyle.Single;
+    public override LineStyle EmphasizedBorderStyle => LineStyle.Double;
+    public override LineStyle SecondaryBorderStyle => LineStyle.Single;
+
+    // All colors are constructed from ColorName16 enum values, so
+    // GetClosestNamedColor16 resolves them to the exact ANSI index
+    // (no nearest-color approximation)
+
+    public override Color Background => new(ColorName16.Black);          // ANSI 0
+
+    public override Color Foreground => new(ColorName16.Gray);           // ANSI 7
+    public override Color ForegroundBright => new(ColorName16.White);    // ANSI 15
+    public override Color ForegroundDim => new(ColorName16.DarkGray);    // ANSI 8
+
+    // Yellow is the closest ANSI color to opcilloscope's signature amber
+    public override Color Accent => new(ColorName16.Yellow);             // ANSI 3
+    public override Color AccentBright => new(ColorName16.BrightYellow); // ANSI 11
+
+    public override Color Border => new(ColorName16.DarkGray);
+    public override Color Grid => new(ColorName16.DarkGray);
+
+    public override Color StatusActive => new(ColorName16.Green);        // ANSI 2
+    public override Color StatusInactive => new(ColorName16.DarkGray);
+    public override Color Error => new(ColorName16.Red);                 // ANSI 1
+    public override Color Warning => new(ColorName16.Yellow);
+
+    // OPC UA Status Colors
+    public override Color StatusGood => new(ColorName16.Green);
+    public override Color StatusBad => new(ColorName16.Red);
+    public override Color StatusUncertain => new(ColorName16.Yellow);
+
+    // Muted text for timestamps, attribution
+    public override Color MutedText => new(ColorName16.DarkGray);
+
+    // Single-line box drawing for clean look
+    public override char BoxTopLeft => '┌';
+    public override char BoxTopRight => '┐';
+    public override char BoxBottomLeft => '└';
+    public override char BoxBottomRight => '┘';
+    public override char BoxHorizontal => '─';
+    public override char BoxVertical => '│';
+    public override char BoxTitleLeft => '┤';
+    public override char BoxTitleRight => '├';
+    public override char TickHorizontal => '┬';
+    public override char TickVertical => '├';
+    public override char TickHorizontalBottom => '┴';
+    public override char TickVerticalRight => '┤';
+    public override char BoxLeftT => '├';
+    public override char BoxRightT => '┤';
+
+    // Minimal decorations matching the other themes
+    public override string ButtonPrefix => "[ ";
+    public override string ButtonSuffix => " ]";
+    public override string TitleDecoration => "───";
+    public override string StatusLive => "◆ LIVE";
+    public override string StatusHold => "◇ HOLD";
+    public override string NoSignalMessage => "· NO SIGNAL ·";
+
+    // Glow uses White which maps cleanly to ANSI 15
+    public override bool EnableGlow => true;
+
+    // Override color schemes - focus highlight uses a DarkGray band since
+    // panel-background shades are not available in the 16-color palette
+    private ColorScheme? _mainColorScheme;
+    private ColorScheme? _menuColorScheme;
+
+    public override ColorScheme MainColorScheme => _mainColorScheme ??= new()
+    {
+        Normal = NormalAttr,
+        Focus = new Attribute(ForegroundBright, new Color(ColorName16.DarkGray)),
+        HotNormal = AccentAttr,
+        HotFocus = new Attribute(AccentBright, new Color(ColorName16.DarkGray)),
+        Disabled = new Attribute(StatusInactive, Background)
+    };
+
+    public override ColorScheme MenuColorScheme => _menuColorScheme ??= new()
+    {
+        Normal = NormalAttr,
+        Focus = new Attribute(Background, Foreground),  // Inverted for menu focus
+        HotNormal = AccentAttr,
+        HotFocus = new Attribute(Background, Accent),
+        Disabled = new Attribute(StatusInactive, Background)
+    };
+}

App/Themes/ThemeManager.cs

@@ -1,3 +1,5 @@
+using Terminal.Gui;
+
 namespace Opcilloscope.App.Themes;
 
 /// <summary>
@@ -14,7 +16,8 @@ public static class ThemeManager
     public static IReadOnlyList<AppTheme> AvailableThemes { get; } = new AppTheme[]
     {
         new DarkTheme(),
-        new LightTheme()
+        new LightTheme(),
+        new TerminalTheme()
     };
 
     /// <summary>
@@ -67,9 +70,28 @@ public static void SetTheme(AppTheme theme)
             handlers = ThemeChanged;
         }
 
+        ApplyTerminalColorMode(themeToUse);
+
         handlers?.Invoke(themeToUse);
     }
 
+    /// <summary>
+    /// Switches the driver between 24-bit color and 16-color ANSI output.
+    /// In 16-color mode the terminal renders colors using its own ANSI
+    /// palette, letting the Terminal theme inherit the terminal's scheme.
+    /// </summary>
+    private static void ApplyTerminalColorMode(AppTheme theme)
+    {
+        Application.Force16Colors = theme.UseTerminalColors;
+
+        // The v2 facade driver caches its own flag rather than reading
+        // Application.Force16Colors, so propagate explicitly when running
+        if (Application.Driver is { } driver)
+        {
+            driver.Force16Colors = theme.UseTerminalColors;
+        }
+    }
+
     /// <summary>
     /// Gets theme names for display in UI.
     /// </summary>

CLAUDE.md

@@ -97,6 +97,7 @@ Opcilloscope/
 │       ├── AppTheme.cs             # Abstract base theme class
 │       ├── DarkTheme.cs            # Dark theme implementation
 │       ├── LightTheme.cs           # Light theme implementation
+│       ├── TerminalTheme.cs        # Theme inheriting the terminal's ANSI palette
 │       ├── ThemeManager.cs         # Global theme state and switching
 │       └── ThemeStyler.cs          # Theme application helper
 │
@@ -207,14 +208,15 @@ Opcilloscope uses JSON-based configuration files with the `.cfg` extension:
 ```
 
 ### Theme System
-Two built-in themes with consistent styling:
+Three built-in themes with consistent styling:
 - **DarkTheme** (default): Dark background, high contrast for terminal use
 - **LightTheme**: Light background for bright environments
+- **TerminalTheme**: Inherits the terminal's own ANSI color palette. Uses only the 16 named ANSI colors (`ColorName16`) and enables `Application.Force16Colors` so the driver emits standard SGR color codes instead of 24-bit RGB — the terminal renders them with its configured scheme. `ThemeManager.SetTheme` toggles `Force16Colors` automatically via `AppTheme.UseTerminalColors`.
 
-Toggle themes via View menu or programmatically:
+Toggle themes via View menu (cycles Dark → Light → Terminal) or programmatically:
 ```csharp
-ThemeManager.SetTheme("Light");
-ThemeManager.SetThemeByIndex(0); // 0 = Dark, 1 = Light
+ThemeManager.SetTheme("Terminal");
+ThemeManager.SetThemeByIndex(0); // 0 = Dark, 1 = Light, 2 = Terminal
 ```
 
 ### Scope View (Multi-Signal Oscilloscope)

README.md

@@ -32,7 +32,7 @@ Browse, monitor, and subscribe to industrial automation data right from your ter
 - **Scope** — Real-time multi-signal oscilloscope (up to 5 signals, 30 s sliding window).
 - **Record** — Export monitored values to CSV. Zero data loss — every server-pushed sample is captured at full precision in a locale-independent format (ISO 8601 timestamps, `.` decimal separator, arrays as semicolon-joined elements).
 - **Configure** — Save/load connection and subscription configs (`.cfg` JSON files).
-- **Themes** — Dark (default) and light.
+- **Themes** — Dark (default), light, and terminal (inherits your terminal's ANSI colour scheme).
 
 <p align="center">
   <img src="docs/theme-dark.png" alt="Dark theme" width="49%">

Tests/Opcilloscope.Tests/App/AppThemeTests.cs

@@ -52,6 +52,7 @@ public void LightTheme_HasLightBackground()
     [Theory]
     [InlineData(typeof(DarkTheme))]
     [InlineData(typeof(LightTheme))]
+    [InlineData(typeof(TerminalTheme))]
     public void AllThemes_HaveNonNullColors(Type themeType)
     {
         var theme = (AppTheme)Activator.CreateInstance(themeType)!;
@@ -73,6 +74,7 @@ public void AllThemes_HaveNonNullColors(Type themeType)
     [Theory]
     [InlineData(typeof(DarkTheme))]
     [InlineData(typeof(LightTheme))]
+    [InlineData(typeof(TerminalTheme))]
     public void AllThemes_HaveNonNullAttributes(Type themeType)
     {
         var theme = (AppTheme)Activator.CreateInstance(themeType)!;
@@ -85,6 +87,7 @@ public void AllThemes_HaveNonNullAttributes(Type themeType)
     [Theory]
     [InlineData(typeof(DarkTheme))]
     [InlineData(typeof(LightTheme))]
+    [InlineData(typeof(TerminalTheme))]
     public void AllThemes_HaveNonNullColorSchemes(Type themeType)
     {
         var theme = (AppTheme)Activator.CreateInstance(themeType)!;
@@ -99,6 +102,7 @@ public void AllThemes_HaveNonNullColorSchemes(Type themeType)
     [Theory]
     [InlineData(typeof(DarkTheme))]
     [InlineData(typeof(LightTheme))]
+    [InlineData(typeof(TerminalTheme))]
     public void AllThemes_HaveSingleLineBoxDrawingCharacters(Type themeType)
     {
         var theme = (AppTheme)Activator.CreateInstance(themeType)!;
@@ -115,6 +119,7 @@ public void AllThemes_HaveSingleLineBoxDrawingCharacters(Type themeType)
     [Theory]
     [InlineData(typeof(DarkTheme))]
     [InlineData(typeof(LightTheme))]
+    [InlineData(typeof(TerminalTheme))]
     public void AllThemes_HaveUIDecorations(Type themeType)
     {
         var theme = (AppTheme)Activator.CreateInstance(themeType)!;
@@ -127,6 +132,66 @@ public void AllThemes_HaveUIDecorations(Type themeType)
         Assert.NotNull(theme.NoSignalMessage);
     }
 
+    [Fact]
+    public void TerminalTheme_HasCorrectName()
+    {
+        var theme = new TerminalTheme();
+        Assert.Equal("Terminal", theme.Name);
+    }
+
+    [Fact]
+    public void TerminalTheme_HasCorrectDescription()
+    {
+        var theme = new TerminalTheme();
+        Assert.Equal("Inherits the terminal's ANSI color palette", theme.Description);
+    }
+
+    [Fact]
+    public void TerminalTheme_UsesTerminalColors()
+    {
+        var theme = new TerminalTheme();
+        Assert.True(theme.UseTerminalColors);
+    }
+
+    [Theory]
+    [InlineData(typeof(DarkTheme))]
+    [InlineData(typeof(LightTheme))]
+    public void NonTerminalThemes_DoNotUseTerminalColors(Type themeType)
+    {
+        var theme = (AppTheme)Activator.CreateInstance(themeType)!;
+        Assert.False(theme.UseTerminalColors);
+    }
+
+    [Fact]
+    public void TerminalTheme_AllColorsMapExactlyToAnsiColors()
+    {
+        var theme = new TerminalTheme();
+
+        // Every color must round-trip exactly through the 16-color ANSI map
+        // so the terminal's own palette is used without approximation
+        var colors = new[]
+        {
+            theme.Background, theme.Foreground, theme.ForegroundBright,
+            theme.ForegroundDim, theme.Accent, theme.AccentBright,
+            theme.Border, theme.Grid, theme.StatusActive, theme.StatusInactive,
+            theme.Error, theme.Warning, theme.StatusGood, theme.StatusBad,
+            theme.StatusUncertain, theme.MutedText
+        };
+
+        foreach (var color in colors)
+        {
+            var roundTripped = new Color(color.GetClosestNamedColor16());
+            Assert.Equal(roundTripped, color);
+        }
+    }
+
+    [Fact]
+    public void TerminalTheme_UsesAnsiBlackBackground()
+    {
+        var theme = new TerminalTheme();
+        Assert.Equal(new Color(ColorName16.Black), theme.Background);
+    }
+
     [Fact]
     public void DarkTheme_HasErrorColor()
     {
@@ -222,6 +287,7 @@ public void ButtonDecorations_AreMinimal()
     [Theory]
     [InlineData(typeof(DarkTheme), "Dark")]
     [InlineData(typeof(LightTheme), "Light")]
+    [InlineData(typeof(TerminalTheme), "Terminal")]
     public void AllThemes_NameMatchesExpected(Type themeType, string expectedName)
     {
         var theme = (AppTheme)Activator.CreateInstance(themeType)!;
@@ -264,6 +330,7 @@ public void MenuColorScheme_HasAllRequiredProperties()
     [Theory]
     [InlineData(typeof(DarkTheme))]
     [InlineData(typeof(LightTheme))]
+    [InlineData(typeof(TerminalTheme))]
     public void AllThemes_UseDoubleBorderAndSingleFrame(Type themeType)
     {
         var theme = (AppTheme)Activator.CreateInstance(themeType)!;
@@ -277,6 +344,7 @@ public void AllThemes_UseDoubleBorderAndSingleFrame(Type themeType)
     [Theory]
     [InlineData(typeof(DarkTheme))]
     [InlineData(typeof(LightTheme))]
+    [InlineData(typeof(TerminalTheme))]
     public void AllThemes_HaveStatusColors(Type themeType)
     {
         var theme = (AppTheme)Activator.CreateInstance(themeType)!;
@@ -291,6 +359,7 @@ public void AllThemes_HaveStatusColors(Type themeType)
     [Theory]
     [InlineData(typeof(DarkTheme))]
     [InlineData(typeof(LightTheme))]
+    [InlineData(typeof(TerminalTheme))]
     public void AllThemes_HaveConnectionIndicators(Type themeType)
     {
         var theme = (AppTheme)Activator.CreateInstance(themeType)!;