The htmLawed module uses the htmLawed PHP library to restrict and purify HTML for security and compliance with web standards and admin policy.
N1ED module for Drupal 7/8/9 is a multiplugin for CKEditor 4. The most important of its featues are:
...and many more useful tools.
Integrate color module support in drupal 8 custom theme
Theming guide for Drupal. You can browse contributed themes or build a custom theme for your site.