Taking what I was talking about a litttle further to explain to Sakura, here is a section of a pen and ink drawing done with black micron pens and diluted ink done with a paintbrush. The blue circles highlighted show areas of softer black, this is the effect that would be so powerful to artist. Its still black ink, its just slight diluted - so to speak.
You can see throughout the drawing the effect of the lighter ink, it really adds to the quality of the final look, without it the drawing would not be the same. There is no color in the lineup that really reflects this effect which to me as a pen and ink artist is very powerful and part of my kit. The grays offered are more true grays, that stand apart from ink work and doesn't blend as well.
I am hoping someone from Sakura can see the power of such pens, I am sure they would sell...