The suggestion about the Nikon sRGB profile concerns the settings of Capture NX-D. Once you set sRGB, Adobe RGB or ProPhoto RGB as your working space in NX-D, you need to restart that program, look for the temp folder where the Nikon .icm profile resides and copy it somewhere. Rename the extension to .icc so that dt can use it (and you can re-name the profile to something shorter than the long, cryptic name NX-D gives it).
Then place that file in the darktable\color\in folder and re-start darktable. You’ll need to use the “unbreak input profile” module. The settings that work for me are: linear (0), gamma (0.4500). You’ll also need to look into the base curve module and reset it to linear (or switch it off).
It works for me for my Nikon Coolpix A, darktable 2.4.4 (Windows), Capture NX-D 1.5.