Edit: I had unthinkingly written, ". . . hard to match with any other water-resistant blue ink . . . ," when I knew that PR American Blue is not very water-resistant. :doh:
PR American Blue is a hard shade to match with any water-resistant blue ink "straight out of the bottle," as of today, especially if you don't want
any of the dyes to run in water. Jlgreer's suggestion of mixing with Iraqi Indigo is a good one; your existing bottle of Luxury Blue, or any of the Noodler's/Swisher "Waterproof" or "SwishMix" blue colors might be good candidates for such a pairing.
About mixing with Noodler's Black: when diluted, N's Black leans a little toward yellow-brown, so any mixing with blue would create a product that leans toward green (see N's Blue-Black, which I enjoy and which leans a lot toward green, and N's Midnight Blue, which leans a tiny bit toward green; also, their blue components are very washable). Iraqi Indigo alone, or with a very small amount of N's Black, is better for darkening a blue ink than N's Black alone.
If you have a Pilot or Namiki cartridge/converter pen, Pilot/Namiki Blue-Black is a high-contrast blue-gray (easy to read, but not like PR American Blue at all) that doesn't run at all in water

. Unfortunately, this ink comes only in the proprietary Pilot/Namiki cartridges

.
Has anybody water-tested Rohrer & Klingner Blau Permanent ('Permanent Blue')?