Not colors, letters or numbers would be better. But I agree that there should be no heredity. Maybe, though, if your alliance is especially large and needs more classes of top-secret items, you should be able to create as many access levels as necessary for you. You will only start at 5 access levels default.
In addition to the following permissions for people who have access to a particular forum: 1) read-only 2) read and write, there should be a third permission, called Create Forum. Through this it would not be dependent on leadership status whether or not you could create a forum. This is because although you may trust someone to lead your alliance, you may not trust them to make forums, and vice versa.