https://microbenotes.com/ziehl-neelsen-staining

Hello Daniel, actually it makes no sence to counterstain with a lipid stain like Sudan Black, because you have to disturb the strong lipid wall of the bacilis during the staining peocedure. You can try instead of Methylenblue as a counter stain tu use Sudan Black. After the last rinse in distilled water put the slides for few dipps in 70% Ethanol (ETOH) then put them in 1% Sudan Black (1 g in 100 ml 70% ETOH) for 5 - 10 min, rinse in distilled water. Check under microscop the staining quality. If it is too black differenciate in 70% ETOH (just few dipps). The link above shows how to proceede the Ziehl-Neelsen-Stain. Good luck!