diff --git a/ns3 b/ns3
index e54f0f069..b2f77f25d 100755
--- a/ns3
+++ b/ns3
@@ -1391,7 +1391,8 @@ def main():
     refuse_run_as_root()
 
     # Enable colorized output for CMake and GCC/Clang
-    os.environ["CLICOLOR"] = "1"
+    if os.getenv("CLICOLOR") is None:
+        os.environ["CLICOLOR"] = "1"
 
     # If pybindgen exists in the parent directory
     # (e.g. ns3-all-in-one), add it to the PYTHONPATH
diff --git a/utils/tests/test-ns3.py b/utils/tests/test-ns3.py
index ffa42972c..91b4a1ace 100755
--- a/utils/tests/test-ns3.py
+++ b/utils/tests/test-ns3.py
@@ -68,6 +68,10 @@ def run_ns3(args, env=None, generator=platform_makefiles):
                 shutil.rmtree(leftover, ignore_errors=True)
     if " -G " in args:
         args = args.format(generator=generator)
+    if env is None:
+        env = {}
+    # Disable colored output by default during tests
+    env["CLICOLOR"] = "0"
     return run_program(ns3_script, args, python=True, env=env)
 
 
@@ -2662,9 +2666,8 @@ class NS3ExpectedUseTestCase(NS3BaseTestCase):
         return_code2, stdout2, stderr2 = run_ns3('run sample-simulator --command-template " "')
         return_code3, stdout3, stderr3 = run_ns3('run sample-simulator --command-template "echo "')
         self.assertEqual((return_code1, return_code2, return_code3), (1, 1, 1))
-        self.assertIn("not all arguments converted during string formatting", stderr1)
-        self.assertEqual(stderr1, stderr2)
-        self.assertEqual(stderr2, stderr3)
+        for stderr in [stderr1, stderr2, stderr3]:
+            self.assertIn("not all arguments converted during string formatting", stderr)
 
         # Command templates with %s should at least continue and try to run the target
         return_code4, stdout4, _ = run_ns3('run sample-simulator --command-template "%s --PrintVersion" --verbose')