I'm the opposite of the above opinions. I like virtually no roast character. Close your eyes, take a sip, and you wouldn't know its 'black'. Messes with your mind, maaaan...
If you're going with huskless black malt, I like Briess Blackprinz. Less ashtray flavors (at least when I chew on them).
You can also use Sinamar, which is like concentrated Carafa special malt extract. I know some brewers use it to adjust color, or as the sole source of color, in the keg.
It doesn't take much Carafa special / Blackprinz to make the beer black, so you should have less of a pH change than in your normal stouts/porters, which (generally) have more roast malt. Relax, read and adjust if needed.