I've had pretty good luck with Noodler's Heart of Darkness as my black permanent ink. I usually prefer blue ink, and Monterverde Documental looks nice to me for a permanent blue ink, and the HOD is a very nice dark black ink.That is what happened to my Noodler's Black. It's degraded to being a "washed out" black. And it doesn't look bad. One just expects a denser black for the OG Noodler's ink. For grey I've got Noodler's Lexington Gray. Wanted a permanent grey and got one with the Lexington.
I think a grey ink would look very nice, and plan on trying some soon.