Looks like a Sepia to me.
There is a wide color spectrum in sepia inks from gray to brown....in some are made traditionally from cuttlefish.
MB Toffee is about that shade....give or take.
As suggested Pelikan Smoky Quartz is not quite a match....but an ink one 'needs', and Herbin Lie de Thee is even lighter but again an ink one should have. Both are very good shading inks, if you are using 90g or + papers.
I've got R&K sepia, not yet used, but that is a different color from my reading more grayish, to grayish- brown....and is an ink that requires getting a pen very clean, in that ink don't mix at all. The company warns about that.....more than likely why I've not tried it.
I might needle load an empty cartridge, in using a rubber bulb syringe cleans out a C/C pen clean quickly.
My 'go to' sepia is the discontinued MB Sepia.
German vintage '50-70 semi-flex stubs and those in oblique give the real thing in On Demand line variation. Modern Oblique is a waste of money for a shadow of line variation. Being too lazy to Hunt for affordable vintage oblique pens, lets you 'hunt' for line variation instead of having it.
www.nibs.com/blog/nibster-writes/nibs-germany & https://www.peter-bo...cts/nib-systems,
The cheapest lessons are from those who learned expensive lessons. Ignorance is best for learning expensive lessons.