Consider the administration part of a web application. I want to display the list of all users, with a hierarchical structure like this:
admin 1 - sub admin 1 - sub admin 2 - simple user 1 - simple user 2 - sub admin 3 - simple user 3 ...
The application is organized as follows; There are admins, sub-admins and simple users. The admins can manage everybody, the sub-admins can manage the users, and the users have no access to admin related privileges.
My goal is to add a small icon on the left of each user, in order to add clarity to the structure (even though the left padding already makes it quite clear). I was thinking of a simple silhouette.
So my question here is: How to differentiate the icons (silhouettes) of the admins, the sub-admins and the users using the same graphical basis? Is there a recurrent color code in web applications (e.g. red for admin, green for subs and blue for users) that I could use, or is there another simple way (and graphically as simple as possible) to make it clear who is what?
When googling for icons, the main idea for "admin" users icons is to add a small key to the silhouette. There are some existing threads but not really what I am looking for: Most appropriate icon for user responsibilities?
Any help would be much appreciated!