diff --git a/src/app.rs b/src/app.rs
index 142cd4c..9a701c5 100644
--- a/src/app.rs
+++ b/src/app.rs
@@ -8,6 +8,7 @@ use crate::output::Logger;
 use crate::state::StateStore;
 use crate::theme::{self, Theme};
 use anyhow::{anyhow, Context, Result};
+use std::cell::Cell;
 use std::io::{IsTerminal, Write};
 use std::path::PathBuf;
 
@@ -20,8 +21,9 @@ pub struct App {
     pub catalog: Catalog,
     pub state: StateStore,
     pub log: Logger,
-    /// Active output color theme.
-    pub theme: &'static Theme,
+    /// Active output color theme (switchable at runtime with the REPL
+    /// 'theme <name>' command).
+    theme: Cell<&'static Theme>,
 }
 
 #[derive(Debug, Clone)]
@@ -90,7 +92,7 @@ impl App {
             catalog,
             state,
             log,
-            theme,
+            theme: Cell::new(theme),
         })
     }
 
@@ -111,7 +113,12 @@ impl App {
     }
 
     pub fn theme(&self) -> &'static Theme {
-        self.theme
+        self.theme.get()
+    }
+
+    /// Switch the active theme (used by the REPL 'theme <name>' command).
+    pub fn set_theme(&self, theme: &'static Theme) {
+        self.theme.set(theme);
     }
 
     /// Ask the user for confirmation on stderr. Accepts y/yes/o/oui.
diff --git a/src/help.rs b/src/help.rs
index 5e9cb22..cffe5a4 100644
--- a/src/help.rs
+++ b/src/help.rs
@@ -508,6 +508,23 @@ pub static HELP_SPECS: &[HelpSpec] = &[
             HelpExample { desc: "Show version and build information.", code: "version" },
         ],
     },
+    HelpSpec {
+        name: "theme",
+        category: "Shell",
+        usage: "theme {flags} [name]",
+        about: "Show the color themes, or switch the active one inside the shell.",
+        search_terms: &["color", "colors", "palette"],
+        flags: &[],
+        subcommands: &[],
+        parameters: &[
+            HelpParam { name: "name", typ: "string", desc: "Theme to switch to (default, ocean, sunset, forest, dracula, mono); omit to list them" },
+        ],
+        io: None,
+        examples: &[
+            HelpExample { desc: "List the available themes.", code: "theme" },
+            HelpExample { desc: "Switch to the ocean theme.", code: "theme ocean" },
+        ],
+    },
     HelpSpec {
         name: "ls",
         category: "Shell",
@@ -751,8 +768,15 @@ fn io_table(input: &str, output: &str, theme: &Theme, color: bool) -> String {
             line
         }
     };
+    let bar = |s: &str| -> String {
+        if color {
+            theme.frame(s)
+        } else {
+            s.to_string()
+        }
+    };
     let row = |cells: &[&str], bold: bool| -> String {
-        let mut line = String::from("│");
+        let mut line = bar("│");
         for (i, c) in cells.iter().enumerate() {
             line.push(' ');
             let text = if bold {
@@ -767,7 +791,7 @@ fn io_table(input: &str, output: &str, theme: &Theme, color: bool) -> String {
             line.push_str(&text);
             line.push_str(&" ".repeat(widths[i] - c.chars().count()));
             line.push(' ');
-            line.push('│');
+            line.push_str(&bar("│"));
         }
         line
     };
diff --git a/src/output.rs b/src/output.rs
index b6d7078..5f514ff 100644
--- a/src/output.rs
+++ b/src/output.rs
@@ -213,6 +213,11 @@ pub fn kv_table(
             s.to_string()
         }
     };
+    let bar = if color {
+        theme.frame("│")
+    } else {
+        "│".to_string()
+    };
     let mut out = String::new();
     out.push_str(&border('╭', '┬', '╮'));
     out.push('\n');
@@ -220,7 +225,7 @@ pub fn kv_table(
         let key = paint(k, color, crate::theme::Theme::key);
         let val = paint(v, color, crate::theme::Theme::val);
         out.push_str(&format!(
-            "│ {} │ {} │\n",
+            "{bar} {} {bar} {} {bar}\n",
             pad(key.as_str(), key_w),
             pad(val.as_str(), val_w)
         ));
diff --git a/src/repl.rs b/src/repl.rs
index 950500b..4621905 100644
--- a/src/repl.rs
+++ b/src/repl.rs
@@ -50,8 +50,9 @@ pub struct AmCompleter {
     /// Short descriptions shown next to candidates in the Tab menu
     /// (Nushell-style).
     descriptions: BTreeMap<String, String>,
-    /// Active color theme (used by the boxed menu highlight).
-    theme: &'static crate::theme::Theme,
+    /// Active color theme (used by the boxed menu highlight; follows the
+    /// app theme when it is switched with the REPL 'theme <name>' command).
+    theme: std::cell::Cell<&'static crate::theme::Theme>,
 }
 
 /// One-line descriptions for the Tab completion menu.
@@ -75,6 +76,7 @@ const COMMAND_DESCRIPTIONS: &[(&str, &str)] = &[
     ("export", "backup config + state"),
     ("import", "restore a backup"),
     ("shell", "show or switch the system shell"),
+    ("theme", "show or switch the color theme"),
     ("ls", "list files and directories (Nushell-style)"),
     ("dir", "list files and directories (same as ls)"),
     ("cd", "change directory — Tab completes folders"),
@@ -88,12 +90,17 @@ const COMMAND_DESCRIPTIONS: &[(&str, &str)] = &[
 
 impl AmCompleter {
     pub fn new(app: &App) -> Self {
-        let mut completer =
+        let completer =
             Self::from_catalog(&app.catalog, &app.config.aliases, &app.config.groups);
-        completer.theme = app.theme();
+        completer.theme.set(app.theme());
         completer
     }
 
+    /// Point the menu at a new theme (after 'theme <name>' in the REPL).
+    pub fn set_theme(&self, theme: &'static crate::theme::Theme) {
+        self.theme.set(theme);
+    }
+
     pub fn from_catalog(
         catalog: &crate::catalog::Catalog,
         aliases: &BTreeMap<String, String>,
@@ -126,12 +133,12 @@ impl AmCompleter {
             descriptions.insert(a.name.clone(), truncate_desc(&desc));
         }
         Self {
-            theme: crate::theme::default_theme(),
+            theme: std::cell::Cell::new(crate::theme::default_theme()),
             commands: vec![
                 "list", "status", "search", "info", "install", "uninstall", "update",
                 "start", "stop", "restart", "run", "doctor", "config", "completion",
-                "self-update", "self-uninstall", "export", "import", "shell", "ls", "dir",
-                "cd", "ps", "where", "get", "help", "version", "exit",
+                "self-update", "self-uninstall", "export", "import", "shell", "theme",
+                "ls", "dir", "cd", "ps", "where", "get", "help", "version", "exit",
             ],
             config_sub: vec!["show", "path", "edit", "validate", "add"],
             shells: vec!["bash", "zsh", "fish", "powershell", "elvish"],
@@ -178,6 +185,12 @@ impl AmCompleter {
                 "shell" => {
                     pool = self.gateway_shells.iter().map(|s| s.to_string()).collect();
                 }
+                "theme" => {
+                    pool = crate::theme::names()
+                        .iter()
+                        .map(|s| s.to_string())
+                        .collect();
+                }
                 "cd" | "chdir" => {
                     // Complete directories only — dive one level per Tab.
                     let cwd = current_dir();
@@ -340,18 +353,21 @@ impl Highlighter for AmCompleter {
         use std::borrow::Cow;
         let _ = completion;
         match candidate.chars().next() {
-            Some('╭') | Some('╰') | Some('├') => Cow::Owned(self.theme.frame(candidate)),
+            Some('╭') | Some('╰') | Some('├') => Cow::Owned(self.theme.get().frame(candidate)),
             Some('│') => {
                 let cells: Vec<&str> = candidate.split('│').collect();
                 if cells.len() >= 4 {
                     if cells[1].trim() == "name" && cells[2].trim() == "description" {
-                        Cow::Owned(self.theme.hdr(candidate))
+                        Cow::Owned(self.theme.get().hdr(candidate))
                     } else {
+                        let bar = self.theme.get().frame("│");
                         Cow::Owned(format!(
-                            "│{}│{}│{}",
-                            self.theme.acc(cells[1]),
+                            "{}{}{}{}{}",
+                            bar,
+                            self.theme.get().acc(cells[1]),
+                            bar,
                             cells[2],
-                            cells[3]
+                            bar
                         ))
                     }
                 } else {
@@ -459,8 +475,6 @@ pub fn banner_box(
 ) -> String {
     let w = BOX_WIDTH;
     let mut rows: Vec<String> = Vec::new();
-    let inner = |content: String| format!("│ {} │", pad_visible(content, w));
-    let blank = || inner(" ".to_string());
     let frame = |s: &str| -> String {
         if color {
             theme.frame(s)
@@ -468,6 +482,15 @@ pub fn banner_box(
             s.to_string()
         }
     };
+    let inner = |content: String| {
+        format!(
+            "{} {} {}",
+            frame("│"),
+            pad_visible(content, w),
+            frame("│")
+        )
+    };
+    let blank = || inner(" ".to_string());
 
     // Top border with the centered header (title in the theme header color,
     // border in the theme frame color).
@@ -574,7 +597,7 @@ pub fn banner_box(
             .to_string(),
     ));
     rows.push(inner(
-        "  shell      ls · cd · ps · where · get · shell · help · version · exit".to_string(),
+        "  shell      ls · cd · ps · where · get · shell · theme · help · version · exit".to_string(),
     ));
 
     // Stats footer.
@@ -894,6 +917,11 @@ fn run_with_editor(app: &App, session: &mut ShellSession) -> Result<i32> {
                 let t = Instant::now();
                 let result = handle_input(app, session, &mut last, &trimmed);
                 last_duration = Some(t.elapsed());
+                // 'theme <name>' may have switched the app theme: repoint the
+                // completion menu at the new palette.
+                if let Some(h) = rl.helper_mut() {
+                    h.set_theme(app.theme());
+                }
                 match result {
                     Ok(true) => break,
                     Ok(false) => {}
@@ -958,6 +986,10 @@ fn handle_input(
             crate::help::print_version(app);
             return Ok(false);
         }
+        "theme" | "/theme" => {
+            theme_command(app, None);
+            return Ok(false);
+        }
         _ => {}
     }
     // Slash commands (Hermes-style).
@@ -968,6 +1000,7 @@ fn handle_input(
         };
         match cmd {
             "shell" => shell_command(session, arg),
+            "theme" => theme_command(app, arg),
             "help" => match arg {
                 Some(topic) => {
                     if let Err(e) = crate::help::print_command(app, topic) {
@@ -1040,6 +1073,11 @@ fn handle_line(
         crate::help::print_version(app);
         return Ok(false);
     }
+    // theme | theme <name>: list the themes or switch the active one.
+    if cmd == "theme" {
+        theme_command(app, rest.first().map(|s| s.as_str()));
+        return Ok(false);
+    }
 
     // Session directory change: kept in the am process, not a child shell.
     if matches!(cmd, "cd" | "chdir") {
@@ -1205,7 +1243,7 @@ fn handle_line(
 fn is_shell_command(word: &str) -> bool {
     matches!(
         word,
-        "ls" | "dir" | "ps" | "where" | "get" | "cd" | "shell" | "help" | "version" | "exit"
+        "ls" | "dir" | "ps" | "where" | "get" | "cd" | "shell" | "theme" | "help" | "version" | "exit"
     )
 }
 
@@ -1368,6 +1406,59 @@ fn shell_command(session: &mut ShellSession, arg: Option<&str>) {
     }
 }
 
+/// 'theme' in the REPL: list the themes, or switch with 'theme <name>'.
+fn theme_command(app: &App, arg: Option<&str>) {
+    match arg.map(str::trim).filter(|s| !s.is_empty()) {
+        None => print_theme_status(app),
+        Some(name) => match crate::theme::find(name) {
+            Some(t) => {
+                app.set_theme(t);
+                let color = app.color();
+                println!(
+                    "{} {}",
+                    if color { t.hdr("theme:") } else { "theme:".to_string() },
+                    format!("{} — {}", t.acc(t.name), t.title)
+                );
+            }
+            None => app.log.error(format!(
+                "unknown theme '{name}' — available: {}",
+                crate::theme::names().join(", ")
+            )),
+        },
+    }
+}
+
+/// List the available themes, highlighting the active one.
+fn print_theme_status(app: &App) {
+    let theme = app.theme();
+    let color = app.color();
+    let hdr = |s: &str| -> String {
+        if color {
+            theme.hdr(s)
+        } else {
+            s.to_string()
+        }
+    };
+    println!("{}", hdr("Theme"));
+    println!(
+        "  ◉ {} — {}",
+        theme.acc(theme.name),
+        theme.title
+    );
+    let others: Vec<&str> = crate::theme::THEMES
+        .iter()
+        .map(|t| t.name)
+        .filter(|n| *n != theme.name)
+        .collect();
+    println!("  {}", theme.dimmed(&format!("⇄ {}", others.join(" · "))));
+    println!(
+        "  {}",
+        theme.dimmed(
+            "'theme <name>' to switch · '--theme <name>' or settings.theme to change the default"
+        )
+    );
+}
+
 fn print_shell_status(session: &ShellSession) {
     let others: Vec<&str> = session
         .available
diff --git a/src/tables.rs b/src/tables.rs
index 4a26c38..efc701b 100644
--- a/src/tables.rs
+++ b/src/tables.rs
@@ -153,8 +153,17 @@ impl DataTable {
             line.push(right);
             line
         };
+        let bar = |s: &str| -> String {
+            if !color {
+                return s.to_string();
+            }
+            match theme {
+                Some(t) => t.frame(s),
+                None => s.to_string(),
+            }
+        };
         let row_line = |row: &[String], header: bool| -> String {
-            let mut line = String::from("│");
+            let mut line = bar("│");
             for (i, c) in row.iter().enumerate().take(all_widths.len()) {
                 line.push(' ');
                 let cell = fit_cell(c, all_widths[i]);
@@ -168,7 +177,7 @@ impl DataTable {
                 };
                 line.push_str(&rendered);
                 line.push(' ');
-                line.push('│');
+                line.push_str(&bar("│"));
             }
             line
         };