I have had no luck with any of the Noodler's waterproof blacks on watercolor paper, just as a word of caution. I bought a huge bottle of Heart of Darkness and it bled like crazy, no matter how long I let it dry. (I'm talking weeks here.) Same for Bulletproof Black. I think the heavy sizing on watercolor paper keeps the ink from interacting directly with the cellulose fibers. (This chemical reaction is what makes the Noodlers inks waterproof, and it's fine on standard office papers. Just isn't as successful on specialty papers.)
I have tested a whole bunch of different pens for use with watercolor washes, and here are some of my results:
Sakura Micron series -- waterproof
Uniball Signo series -- waterproof. (Uniball makes most of its pens with ultra-secure ink that prevents forgery, and they are all really wonderful for artwork.) These sometime need a couple minutes to fully dry, if you've applied to heavily sized paper.
Pilot Hi-Tec-C -- bleeds when wet
Pentel Energel -- bleeds when wet
Pilot Address Pens -- waterproof, deepest black I've seen. (Available from Jet Pens http://www.jetpens.com/Pilot-Envelop...nk-Pens/ct/953
Amazing drawing pens.)
Zebra Sarasa series -- waterproof
Prisma Premier technical pens -- waterproof
Pentel Technica pens -- waterproof. They go on very wet, and you need to let them dry a couple minutes on heavily sized papers.
Pentel Sicci pens -- bleeds when wet
Pitt artist pens -- waterproof
Copic Multiliners -- waterproof. (The professional-level SP series have extremely rugged points, and can be refilled when ink runs out.)
Pilot G2 -- bleeds when wet
Pentel Pocket Brush Pen -- waterproof. Goes on wet, sometimes needs to dry a couple minutes
Tachikawa Comic Nib Fountain Pen -- exceptionally waterproof. Very fine line. (http://www.jetpens.com/Tachikawa-Com...ck-Ink/pd/4577
) I have two of these pens and love them to death. They're a bit rougher than gel pens when writing, but the nib is slightly flexible and the subtle line variation is very expressive. Refillable.
Rotring Tikky Graphic pigmented ink -- waterproof. A technical pen design similar to the Sakura Micron, but it's a bit wetter and more robust to write with. (At least for me.) (http://www.jetpens.com/Rotring-Tikky...ck-Ink/pd/7835
Platinum Carbon fountain pen ink -- waterproof, fountain-pen compatible. I've always got 2 or 3 fountain pens on my desk inked up with this. A bottle costs a ton, but lasts forever. It also comes in cartridges that cost less up front.
Hope this helps.