Is it the just hard shell which is turning black? I grew a mango from a pit and they they have composite seeds. Each Mango has 2-3 seeds inside of a single pit.

It was a year and a half ago, so I'm not sure exactly what method I used. But, I think I removed the hard shell first, then left the inner part between moist paper towels. Here's a pic from when it germinated.

A mango has its seed inside. They are either mono-embryonic or poly-embryonic. If the seed you have is poly....2 or 3 seeds inside the pit, you will get a clone of the fruit it came from. If it's a mono..single, it will not be the same but rather a hybrid of the fruit it came from. What it will taste like only Mother Nature knows.