I am really glad I found this post. I made Moroccan Preserved Lemons at least 10 years ago and they have turned black and look just like the ones in the post. I don't know why they turned black--I thought that maybe all the acid from my canning jars corroded the lid and interacted with the metal somehow. However, I have continued to use them anyway and so far no one from my family has gotten food poisoning, LOL, so I assume they are OK. I use them in my Lemon & Olive Tagine Recipe. I have an Emile Henry Tagine and they have a recipe for preserved lemons, but they suggest adding vinegar to prevent them from turning black...hmm...however, they cover theirs with salted water, whereas I covered mine with 100% lemon juice (and salt.) So, I guess I'll just keep on using them...
