IntelliJ IDEA 9 (Maia) lets you assign custom colors to arbitrary sets of files (Scopes) in Editor tabs or Navigation lists (Go to class/file, etc):
This helps you even more quickly than before understand which class you are looking at: JDK, a library, or your own app. The feature is available in Maia builds that you can get from EAP under Settings/File Colors.
I think it would be useful to have some default schemas. Few people find this feature, but fewer people will spent time to setup their favorite colors.
Personally I would like to use this features from scratches or some default examples, but rather won’t setup it from the very beginning.
In any case, the color tabs and file is a great feature and can be very-very useful.
Andrey, it looks like adding default schemas is a good suggestion. Thanks!