Yeah that's true, I've had dark ones that are ok off my plant. There's a guy in the town below us that has one that is completely different than the one I have. It's leaves are different, it ripens differently, its fruits are more glossy and it's like a mango yellow inside. I'd go out on a limb and say it's a different species. He's going to give me some cuttings so I can graft into mine.
I'll agree with you on the miracle fruit thing with one thing I tried, beer with lime juice. Jesus, it was like an overly sweet Smirnoff ice or something like that. The fruit I have, weirdly, only acts on sour stuff. It doesn't make sweet things taste sweeter. I've tried others that do make everything sweeter