Support coloring entire message with the user color (#193)

src/tests.rs

@@ -196,6 +196,7 @@ pub fn mock_tunables() -> TunableValues {
         .collect::<HashMap<_, _>>(),
         open_command: None,
         username_display: UserDisplayStyle::Username,
+        message_user_color: false,
         image_preview: None,
     }
 }