Since I hadn't tried it before, I bought a 10 ml bottle, but it also comes in a 30 ml, which I'll buy next time. It also come in cartridges designed for the J. Herbin roller ball pen.
Vert Olive is a light color, but it shades nicely. The scan of the writing example below came out a bit yellower than the true color, but it show the shading very well. This writing example above was written in a Clairefontaine Roadbook and the on below was done on Clairefontaine GraF it dot grid paper. The shading occurred more readily on the GraF it, so paper may make a big difference.
The drawing below was drawn and colored using only Vert Olive. The range of color comes from lightness of touch, plus the ink darkens quickly when you layer over previously applied color.
The weather here has been windy, and I've noticed that all my inks seem dryer than usual. Still both my Lierre Sauvage and Vert Empire seemed wetter, and I know the Vert Empire is 'wet', so I believe Vert Olive is middle of the road--neither a 'wet' or a 'dry' ink.
Personally, I like the color. You can often get an olive by mixing yellow and black, and it shows in Vert Olive. At its lightest, it is a yellowy green. When you go darker with it, you see the hints of black. I have no idea what colors J. Herbin actually used in the formulation, but they certainly convince my eye that both colors are here.