This is the text of a suggestion I filed in the kde forum a long time ago. 
Since the contributions there are mostly ignored I post the text here again. 
it is a feature request, not more, not less. 

I have a number of projects defined in kdevelop. This might be separate applications / libraries, but often also different versions of such, for example different branches. Very often I have to open a file from a project different to the one I am currently working on. Or I am working on two projects at the same time, since they depend on each other (e.g. client and server components). It is a great feature of kdevelop to offer handling several projects at once, however this also leads to confusion: often I confuse which project an open file belongs to, for example when the projects contain files with the same name. Currently the only way to clearly see which project an opened file belongs to is by reading the windows title when having the open file in focus. This is very inconvenient. 

My suggestion: 
Enhance the project options by an optional background color. That color would be used at two places: in the project manager side bar and in the tabs on top of the open files. This would allow an intuitive association of files to their project. 


Reproducible: Always