This would be an easy to implement yet powerful feature.
We have a bunch of modules (>100), and every module is either j2se or j2me. When I open some unknown class, first thing I do is a best guess what type of code is that? Is that for j2se or j2me? It may not be straightforward what java does the class use, because there are many classes that are named the same (e.g. java.util.Vector), and time should be spend on getting a really basic context information.
A name of the module doesn't say me much. My suggestion would be to have a different highlighting for modules. Just a different background for every module will do. Or these colors may be assigned depending on 'module type'. E.g. modules could be 'classified' by the project subsystem ("Frontend", "Backend".. ) or by some other criteria, and every 'type' would have its features like background. That's enough to carry information and save a lot of time! Why not assign an icon to the module/module type? A project view would be more informative...
Any chance to see something like that?
(Clarification: in my case, j2me parts are set up as 'java modules with no JDK' and therefore have the same icons in project view. It cannot be done the other way because of the very special java we use which can not be set up as JDK in Idea)