Aperture usually has one Master photo file in a Project (yellow) like "All Animals", which can be copied into other Albums (blue) like "Birds". The Albums reference the Masters in another location and you can make changes (black & white, saturation) without changing the Master.
You can also Export a Master by right-clicking on the image if you want to duplicate the Master to your desktop (then reimport to a new Project). You may want to change the file name just so you can keep track (ie. IMG_2031a).