diff --git a/.changeset/colorize-stderr-tty.md b/.changeset/colorize-stderr-tty.md
new file mode 100644
index 00000000..d269f8ec
--- /dev/null
+++ b/.changeset/colorize-stderr-tty.md
@@ -0,0 +1,5 @@
+---
+"@googleworkspace/cli": patch
+---
+
+Colorize stderr warnings and errors with ANSI codes when output is a TTY terminal
diff --git a/src/error.rs b/src/error.rs
index 25cc9f59..9ec16ef3 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -15,6 +15,29 @@
 use serde_json::json;
 use thiserror::Error;
 
+pub(crate) fn is_tty() -> bool {
+    use std::io::IsTerminal;
+    std::io::stderr().is_terminal()
+}
+
+fn colorize(s: &str, code: &str) -> String {
+    if is_tty() {
+        // Strip control characters to prevent terminal escape injection.
+        // We allow newline and tab for basic formatting.
+        let sanitized: String = s
+            .chars()
+            .filter(|&c| !c.is_control() || c == '\n' || c == '\t')
+            .collect();
+        format!("\x1b[{code}m{sanitized}\x1b[0m")
+    } else {
+        s.to_string()
+    }
+}
+
+pub(crate) fn yellow(s: &str) -> String { colorize(s, "33") }
+pub(crate) fn red(s: &str) -> String    { colorize(s, "31") }
+pub(crate) fn bold(s: &str) -> String   { colorize(s, "1")  }
+
 #[derive(Error, Debug)]
 pub enum GwsError {
     #[error("{message}")]
@@ -111,7 +134,7 @@ pub fn print_error_json(err: &GwsError) {
     {
         if reason == "accessNotConfigured" {
             eprintln!();
-            eprintln!("💡 API not enabled for your GCP project.");
+            eprintln!("{}", yellow("💡 API not enabled for your GCP project."));
             if let Some(url) = enable_url {
                 eprintln!("   Enable it at: {url}");
             } else {
@@ -126,6 +149,16 @@ pub fn print_error_json(err: &GwsError) {
 mod tests {
     use super::*;
 
+    #[test]
+    fn test_color_helpers_no_ansi_when_non_tty() {
+        // In test runners, stderr is not a TTY — helpers must return the raw string.
+        if !is_tty() {
+            assert_eq!(yellow("x"), "x");
+            assert_eq!(red("x"), "x");
+            assert_eq!(bold("x"), "x");
+        }
+    }
+
     #[test]
     fn test_error_to_json_api() {
         let err = GwsError::Api {
diff --git a/src/executor.rs b/src/executor.rs
index 49101ece..a9d8c007 100644
--- a/src/executor.rs
+++ b/src/executor.rs
@@ -228,7 +228,7 @@ async fn handle_json_response(
                 Ok(result) => {
                     let is_match = result.filter_match_state == "MATCH_FOUND";
                     if is_match {
-                        eprintln!("⚠️  Model Armor: prompt injection detected (filterMatchState: MATCH_FOUND)");
+                        eprintln!("{}", crate::error::yellow("⚠️  Model Armor: prompt injection detected (filterMatchState: MATCH_FOUND)"));
                     }
 
                     if is_match && *sanitize_mode == crate::helpers::modelarmor::SanitizeMode::Block
@@ -254,7 +254,7 @@ async fn handle_json_response(
                     }
                 }
                 Err(e) => {
-                    eprintln!("⚠️  Model Armor sanitization failed: {e}");
+                    eprintln!("{} {e}", crate::error::yellow("⚠️  Model Armor sanitization failed:"));
                 }
             }
         }
diff --git a/src/main.rs b/src/main.rs
index 22259a44..246dac3b 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -174,7 +174,8 @@ async fn run() -> Result<(), GwsError> {
             Ok(fmt) => fmt,
             Err(unknown) => {
                 eprintln!(
-                    "warning: unknown output format '{unknown}'; falling back to json (valid options: json, table, yaml, csv)"
+                    "{} unknown output format '{unknown}'; falling back to json (valid options: json, table, yaml, csv)",
+                    crate::error::yellow("warning:")
                 );
                 formatter::OutputFormat::Json
             }