This is the Iroshizuku ink by Pilot in Fuyu-syogun, available at JetPens. It is a steel-gray blue, definitely a strong color but not bold. It takes awhile to work on your sense of sight, and using it in a medium nib Rotring Surf on Doane Paper makes the color seem even stronger. I had first tried it in a fine nib pen, and didn't like it at all. On no, a dud -- and an expensive dud at that! But a few hours and several Cherry Zero Cokes later I got out a medium nib, filled it up, and...let it sit for a few weeks. And now I have to admit, I really like this color. Dark, brooding skies aren't my style, and I don't gravitate towards battleships. But I am becoming very fond of Fuyu-syogun, as the color seems to have a softer personality than I'd originally noticed.
And I'm also becoming very fond of this Doane Paper. I am not a big fan of grid paper, but the grid+lines format is starting to work for me. My writing would never look this good on lined/unlined paper alone, and I doubt I'd use grid paper because it just seems too free form for my tastes. But this paper is very different, I'm very glad I took the plunge (thanks to The Pen Addict).