Paula Burch's Community of Dyers has a wealth of information on all types of dyeing, including discharge dyeing.
http://www.pburch.net/drupal/?q=forum/23 There is info on which black dyes discharge to which colors, but I'm not sure about commercial black fabrics. Don't rule out non-blacks in your testing. They often have great results, too.
Be aware that manufacturers change their dyes without notice, so a black that may discharge red today could be orange or cream on a sample from a different dye lot down the road...or it may not discharge at all, some dyes don't. Note the Kona 1080 Coal in the photos below (top row second swatch). Very little discharging after over 5 minutes.
Color results will also vary slightly depending on the type of bleaching compound used. In the photos, compare the Soft Scrub vs bleach results, particularly with the yellow swatch (part of that is the density of the application in the bleach sample, but it truly is lighter IRL). Bleach results are sharper, clearer and have no halo. In fact, it is the halo color in the top samples that is the total color in the bottom samples. Not better or worse, just a difference to be aware of.
This is a test bunch of Kona solids discharged with Soft Scrub w/bleach (all are Kona)
and these are the same color fabrics discharged with full strength bleach.