Is there an ready-made solution to mark edited form fields?
I've only seen Track Field Changes, but that doesn't give immediate visual feedback.

Edit: I know you asked for something that was already out in the wild, but the following might be useful.

I guess you could write something custom relatively easily though using jQuery's .change event.

Something like the following I guess (code will need checking but it should be pretty near).

JavaScript

(function ($) {
    Drupal.behaviors.formFieldTracker = {
      attach: function(){
        $(input).change(function(){
          $(this).addClass('field-edited');
        }));
      }
    }
})(jQuery)


Module

function MYMODULE_preprocess_page(&amp;$vars) {
  // Only add the JavaScript on admin pages as defined by hook_admin_paths()
  if (path_is_admin(current_path())) {
    $path = drupal_get_path('module', 'MYMODULE');
    drupal_add_js($path . '/js/MYSCRIPT.js');
    $vars['scripts'] = drupal_get_js();
  }
}


Then you could add whatever CSS you fancy afterwards:

.field-edited:after {
  content: 'Edited';
  display: inline-block;
  color: #F00;
  font-style: italic;
}