This doesn't really tell me anything?
IntelliJ is trying to warn you that you have created a library, but it is not referenced anywhere in the project. It is gently asking "Did you mean to add this library as a dependency?".
The entry is not disabled. It is greyed out to show that it is not referenced in any module as a dependency. Once you add the library to the dependencies list, the color will change.
It is a two-step process:
- Create a library
- Reference new library in a module
Code completion is not working because your module is not aware of the library classes.
Module dependencies
Non-referenced and referenced libraries