Hi Nik,
What you describe is exactly what I see. Once I begin to edit a photo whether in Photos or in Nitro, I see the original color RAW File, and that matches what I see in Preview. I think things are working correctly. Whatever tag Photos uses to create a B&W thumbnail from the RAW just doesn’t get applied to each RAW file imported. At least all the RAW’s are intact an untouched, which is the important thing. For awhile it looked to me that I couldn’t get back the original RAW files.
Thanks again for your help.
Ed