I kinda feel you on the dark thing... maybe dark isnt the word but "woody" or "warm and thick" kinda come to mind. I noticed that both of my RNP's exhibit this character, and compared to something like a MAckie, they dont sound as crispy. A Good thing in my opinion. I keep wanting to feel like the RNP has a "tape-ish" sound to it, which isnt bad at all.
I mate it with a Sennneiser 441 all the time and really get some tape-ish , round warm flavored tones going on, I guess its party cause the 441 doesnt have a lot of high lift, and it takes the RNP most of its gain to get the levels good with a 441, so lots of preamp color in there from doing that I guess, too.
Certainly has a color to it IMO.