Question

I’ve added meta boxes to my posts using the action “add_meta_boxes” to add/change custom settings like background-color, etc.

When I enable the custom fields in my screen options, all values of my meta boxes are displayd in these custom fields!

There are also showing up in the selectbox to add a new “custom field”.

Answer 1

If you want to hide your post meta data from custom fields metabox, you should start your meta keys with underscore. Example _background-color

Added:

Also you can use is_protected_meta filter, which return boolean value (true - hide, false - show).

Filter parameters: $protected, $meta_key. See wp-includes/meta.php file. function is_protected_meta()