Color palettes for content types
Found this after 5 seconds of googling:


https://www.drupal.org/project/color_field
https://www.drupal.org/project/colorfield
https://www.drupal.org/project/jquery_colorpicker


The search query was: drupal color field.




Choose one,
add one color field per content type to the user entity type (users should be able to edit their profile),
then retrieve the current user and the selected values and add them as node class via template_preprocess_node.





  I may have been unclear. I don't want to let each user set their own
  color palette, I want users with the right permissions to be able to
  set the palette for an arbitrary content type for ALL users/anonymous
  users accessing the site. (I'll update my question) – tanbog


For that you need to create a configuration form. @see docs Working with Configuration Forms.

You can get a list of all content types to build your form. @see question Get the list of all content types.

You also may want to use the color FormElement. @see docs class Color.

In the end you probably still use template_preprocess_node, to get the stored config in there, and then set the CSS class according the current node type.