Hello, and thanks for testing!
Unfortunately i can’t give a very scientific answer, because i’m totally ignorant about color science
From what i’ve seen, it seems that the best results are obtained with the standard color profile for your camera, the same that you normally use to develop normal digital pictures.
“No profile” is definitely not a good setting, i always get strong color deviations with that. This is true for my Sony A7, my Sony A6000, but also for many other sample raw files that i got from other users here.
The Nikon D750 profile should be included in RT, so in your case just selecting “Auto-matched camera profile” should be enough. Otherwise, you can look for the suitable DCP profile online, or take it from Adobe DNG Converter.
Be sure to enable all the available checkboxes after selecting the profile, especially “Look Table” and “Tone Curve”.
These have nothing to do with the negative inversion itself, as they come into play later in the processing pipeline.
Working profile is what RT uses internally for calculations, after the picture is already converted to a positive (with happens before demosaic); i always leave the default setting.
Output profile will be the color profile of your output file. This is also not related to negative inversion, but rather to what you plan to do with your output file. If you want to export a tif to do further editing in a different software, you might want to use a wide gamut profile, in order to retain as much color information as possible. Still, i’m not an expert on this, so please take a look at the wiki for more accurate info
There’s no need to match the Working and Output profiles. From what i understand, it’s normal to have the Working profile being wider gamut than the Output, in order to leave more headroom for intermediate color calculations.
Not at all! Feel free to ask, and thanks again for testing
alberto