I got a bottle of Brexit last year at the Commonwealth Pen Show. My batch is a pale and chalky purple (somewhat similar to De Atramentis Jeanne d'Arc and the original Organics Studio Potassium). Basically think of a cross between what the original image that The Good Captain posted (but purple, not blue) and what Dark Audit posted (but a little lighter, although might be the crappy absorbent Piccadilly paper.
On the plus side, it's very fast drying on that paper (between 5 and 10 seconds), and appears to be pretty waterproof. I'm not seeing much of a difference between that and the not watered writing on that paper. I'm also not seeing much of any showthrough/bleedthrough. But the color is really flat looking (I would definitely call it chalky). And it had some spread. The lightness makes it a little hard to read, although I've seen worse inks in that regard). Almost no shading that I'm seeing.
I'm glad I bought it, but I don't think I'd buy another bottle of it.
It reminds me of a lavender version of Upper Ganges Blue for water resistance but also for the blah chalky pale color.
Ruth Morrisson aka inkstainedruth