mkdir -p example_ws/src
cd example_ws/src
git clone https://github.com/InigoMoreno/minimal_ros2_example.git
rosdep install -iy --from-paths .
cd ..
colcon build --symlink-install
source install/setup.bash
Open example_ws/src in vscode
Look at file minimal_ros2_example.py
You should see that the custom msg Colour has no syntax higlighting or field autocompletion, but the std msg Color RGBA does.