The colors of the olives, green, black or dark have nothing to do with the type of the olive tree, but with their ripening.
In the beginning all the olives are green, as very simply, they are still unripe. They have been harvested before the beginning of their ripening cycle.
These olives are harvested from the tree shortly before their complete ripening and are placed immediately in natural brine.
The natural black olives have been harvested following their complete maturing and they have been processed with successive layers of thick sea salt. Black olives can be found in various shapes, something depending on their processing.