It's a vibrant blue and is an archival ink. Cannot remove it and it's impossible to miss when you stain something with it. It'll stain your fingers for days.
If you drop it on a rug, or countertop or spill some while filling or cleaning a pen it's a major pain to clean up, if you can even clean it up.
It also has a reputation for staining the ink reservoir of your pen and if you have a fancy demonstrator to show off the ink you'll only ever see blue and none of the fun colors you're using.
Which is why Noodler's Ink issues a free fountain pen (The Charlie) with the 4.5 oz. eyedropper bottle. You can use that, or you dedicate an inexpensive pen, like a TWSBI Eco or a Pilot Metropolitan to the ink. (Many do this.)
