I checked the packaging for the Maracyn-Two and it does mention B vitamins. The box doesn't really tell much other than the active ingredient is Minocycline. It doesn't list inactive ingredients.
The orange really is orange. It's in odd places such as in between the eyes on one dalmation molly, the top edge of the dorsal fin on another sailfin dalmation molly, and behind the pectoral fins on one of my dalmation fry. Several other dalmation mollies and silver mollies have this. The orange is the color orange of my platys.
Tank details...50 gallon. One Emperor 280 and One Penguin 125 biowheel filters. 3 18" airstones that run off and on throughout the day for a total of about 16 hours. Fake Gravel, fake plants, real fish. It's full of Mollies (assorted colors), platys (assorted) and guppies. Water parameters...almost perfect. Ammonia, nitrates, nitrites are all zero. My pH is slightly alkaline. I have an appropriate amount of aquarium salt added for the tank. The water is crystal clear. I do 25%ish water changes every two to four weeks or as soon as I detect an increase in nitrAtes. I only vacuum about 2/3s of the gravel with each water change.
The other fish deaths were mollies and the last one was a black molly that had LARGE white spots on her. The two largest were right behind her dorsal fin and on the dorsal fin. It looked a bit like a fuzzy depression. She lived for about 3 days looking really bad like that. While continuing to treat the 50 gallon, I moved her to the 3 gal
infirmary. Since she had gotten the full dose of Maracyn, I decided to try Melafix on her. It didn't work.
As of right now, the silver and dalmation mollies still have the orange spots. Not growing. Not going away. They all seem healthy and eat well. I have completed my 10 day treatment of Maracyn-two. I haven't lost any fish since that last black molly. I have a picture of the first fish that died on me at:
I have looked through my fish books and can't find anything about the orange spots, so I was starting to think like you that perhaps it was the medication staining the fish, but it's really staining in an odd pattern of only a scale or two here and there.