I'm lucky to have been given some of this 150 Confederation Brown to (p)review. I'm going to skip the history and background of this ink and for that purpose I refer you to the review of Claudia, the person behind this colour, and also the reviews of Visvamitra and Tas.
As the others have pointed out, this is a complex colour, ranging from murky green to brown, depending on paper and lighting. I find that it seems to be browner, more earthy on more absorbent paper, and veers to a greener tint on less absorbent paper. A great colour with character: just look at the writing samples.
The behaviour, as expected from KWZI, is great: wet flow, smooth and lubricated feel. Not water resistant.
If you're lucky enough to be in Canada, don't miss out the chance to get this amazing ink at Scriptus 2017. If you're not in Canada, you need to invest in some Canadian friends!
(Maruman word card)
(I can't draw, so I'll just provide you with some writing samples. They are done with Pilot 823 FA, Platinum 3776 Music nib - a rather dry pen, and a Pilot Parallel 2.4mm for the letter "C". I'm sorting these samples according to how absorbent the paper is, but that's a very subjective matter of course.)
(The most absorbent: crappy envelop paper. Everything feathers on this paper.)
(Clairefontaine 80g copy paper)
(Maruman looseleaf: look how it's greener already than more absorbent paper like the envelope.)
(Tomoe River: see the green now?)
(Coated, the least absorbent: postcard paper. It turns into a weird greyish green.)
(You'll see why it's difficult to describe this colour. It's something between green and brown.)
(Look at how it reacts with water: you can see how complicated this colour is.)
(Okay now I'm messing around: this is all one ink. With bleach. In contact with bleach this ink turns into a freaky radioactive green, and slowly turns lighter and yellower. I can imagine Nick Stewart doing amazing things with this ink.)