The blackish discoloration on your hands could be post-inflammatory hyperpigmentation, a condition like lichen planus, or a fixed drug reaction to previous medications. Since the symptoms returned after stopping sulfasalazine and roxithromycin, please do not self-medicate, as this can worsen the discoloration. You should consult your dermatologist for a re-evaluation. They may prescribe topical treatments like mild corticosteroid creams, calcineurin inhibitors, or skin-lightening agents to safely fade the spots. Rest assured, this is a very manageable cosmetic concern, but finding the exact cause is essential for a permanent cure.