How to change widget's form color in admin?

Question

I have a simple question. How to change widget's form color in admin panel of wordpress (on widgets page) to make them more unique? Here is a simple example:

Answer 1

Register/enqueue an admin stylesheet

function my_admin_theme_style() {
    wp_enqueue_style('my-admin-theme', get_template_directory_uri().'/admin-style.css');
}
add_action('admin_enqueue_scripts', 'my_admin_theme_style');

Then add rules of the form

#widget-list div[id*="_archives-"], div[id*="_archives-"] {
  background:red;
}

Consider that proof of concept. I will leave it up to you to target the precise elements you want.