Different color icons for different instances of CN

You can always go further and make possible assigning custom icons to the notebook files.

But.. Will be there any need in this feature when tabs/multinotebook are implemented?

Currently I have 4 installations of CN (and planning to make 5th), but I imagine it in future as one instance with 5 tabs..

Take a look at this idea:
http://roadmap.cintanotes.com/feedback/13469-color-scheme-should-affect-all-areas-including-the-icon/

If color scheme also changes the icon to match the scheme's color, then this idea is resolved also.