How to duplicate a project in Final Cut Pro without affecting the original

I have created a project in colour in FCP. I wish to duplicate this project, with all its clips, transitions etc to stand alone, so I can create a black and white version (and still colour edit each clip manually).

I attempted this using Edit>Duplicate, yet the changes I made to the duplicate project also affect the original. This is not what I want to do.

How do I create duplicate that is a standalone project?