fix(tui): use explicit RGB app background

Author: BunsDev

src-rust/crates/tui/src/lib.rs

@@ -351,7 +351,7 @@ mod tests {
     use claurst_core::types::{ContentBlock, Role, ToolResultContent};
     use dialogs::PermissionRequest;
     use notifications::NotificationKind;
-    use ratatui::{backend::TestBackend, buffer::Buffer, layout::Rect, Terminal};
+    use ratatui::{backend::TestBackend, buffer::Buffer, layout::Rect, style::Color, Terminal};
     use std::path::PathBuf;
     use std::sync::Arc;
     use tempfile::tempdir;
@@ -812,6 +812,20 @@ mod tests {
         assert!(rendered.contains("hello"));
     }
 
+    #[test]
+    fn test_render_app_uses_explicit_rgb_background() {
+        let backend = TestBackend::new(120, 40);
+        let mut terminal = Terminal::new(backend).unwrap();
+        let app = make_app();
+
+        terminal
+            .draw(|frame| crate::render::render_app(frame, &app))
+            .unwrap();
+
+        let background_cell = terminal.backend().buffer().cell((10, 20)).unwrap();
+        assert_eq!(background_cell.bg, Color::Rgb(0, 0, 0));
+    }
+
     #[test]
     fn test_render_app_keeps_footer_visible_with_slash_suggestions() {
         let backend = TestBackend::new(120, 30);

src-rust/crates/tui/src/render.rs

@@ -77,6 +77,7 @@ const SPINNER: &[char] = &[
     '\u{2736}', '\u{2733}', '\u{2722}', '\u{00b7}',
 ];
 const CLAUDE_ORANGE: Color = Color::Rgb(233, 30, 99);
+const APP_BACKGROUND: Color = Color::Rgb(0, 0, 0);
 const WELCOME_BOX_HEIGHT: u16 = 9;
 const STATUS_THINKING: &str = "thinking";
 const STATUS_THINKING_ELLIPSIS: &str = "thinking\u{2026}";
@@ -441,10 +442,10 @@ pub fn render_app(frame: &mut Frame, app: &App) {
     let size = frame.area();
     app.last_selectable_area.set(size);
 
-    // Fill the entire frame with a black background so the terminal's default
-    // color (blue on Windows) doesn't bleed through cells not covered by widgets.
+    // Fill the entire frame with explicit RGB black so terminal palette remaps
+    // and default colors do not tint cells not covered by widgets.
     frame.render_widget(
-        Block::default().style(Style::default().bg(Color::Black).fg(Color::White)),
+        Block::default().style(Style::default().bg(APP_BACKGROUND).fg(Color::White)),
         size,
     );