I love Scrivener, and have created several different Projects that I use for my business. I usually have 2 or 3 open at a time, and they all look the same at a glance.
It would be very helpful to give them different colored menu bars. That way, I could see which was which easily, and not interrupt my train of thought when I switch from one Project to another.
Is it possible to include a Menu option for color?
That would be very unorthodox and I don’t think it is even possible for a Mac application to change the menu bar colour at all, let alone for different windows—not that it would help you out with your problem anyway, as it sounds like you are looking for something that would better visually distinguish between open windows. A hypothetical menu bar change wouldn’t occur until after the window was selected.
This is just a general Mac tip, but how are you looking for windows? If you use Application Exposé (Ctrl+Exposé button on keyboard), the name of the project is printed clearly beneath each window so it’s easy to find stuff even if they are overlapping each other normally and obscuring each other’s titles. Application Exposé spreads all windows out so you can better see their individual internal features, too.