Index: test/libcxx/test/config.py
===================================================================
--- test/libcxx/test/config.py
+++ test/libcxx/test/config.py
@@ -91,6 +91,7 @@
         self.configure_env()
         self.configure_compile_flags()
         self.configure_link_flags()
+        self.configure_color_diagnostics()
         self.configure_debug_mode()
         self.configure_warnings()
         self.configure_sanitizer()
@@ -469,6 +470,25 @@
         else:
             self.lit_config.fatal("unrecognized system: %r" % target_platform)
 
+    def configure_color_diagnostics(self):
+        use_color = self.get_lit_conf('color_diagnostics')
+        if use_color is None:
+            use_color = os.environ.get('LIBCXX_COLOR_DIAGNOSTICS')
+        if use_color is None:
+            return
+        if use_color != '':
+            self.lit_config.fatal('Invalid value for color_diagnostics "%s".'
+                                  % use_color)
+        cxx_type = self.cxx.type
+        if cxx_type is None:
+            self.lit_config.warning(
+                'Unable to force color output for unknown compiler "%s"'
+                % cxx.path)
+        elif cxx_type in ['clang', 'apple-clang']:
+            self.cxx.flags += ['-fcolor-diagnostics']
+        elif cxx_type == 'gcc':
+            self.cxx.flags += ['-fdiagnostics-color=always']
+
     def configure_debug_mode(self):
         debug_level = self.get_lit_conf('debug_level', None)
         if not debug_level:
Index: www/lit_usage.html
===================================================================
--- www/lit_usage.html
+++ www/lit_usage.html
@@ -192,6 +192,16 @@
 </blockquote>
 </p>
 
+<p>
+<h3 class="lit-option">color_diagnostics</h3>
+<blockquote class="lit-option-desc">
+Enable the use of colorized compile diagnostics. If the
+<code>color_diagnostics</code> option is specified or the enviroment variable
+<code>LIBCXX_COLOR_DIAGNOSTICS</code> is present then color diagnostics will be
+enabled.
+</blockquote>
+</p>
+
 </div>
 </body>
 </html>