* <li>feature group is not visible, or</li>
* <li>feature values lie outside any colour threshold, or</li>
* <li>feature is excluded by filter conditions</li>
* </ul>
* <li>feature group is not visible, or</li>
* <li>feature values lie outside any colour threshold, or</li>
* <li>feature is excluded by filter conditions</li>
* </ul>