Heat the dark chocolates and condensed milk in a double boiler over medium-low heat until the chocolate is melted and the mixture is smooth. The mixture will have a slight marshmallow texture. Stir in the mint extract to your taste.
Remove from the heat, and then cover and refrigerate until completely cool, at least 2 hours.
Once chilled, roll in teaspoon-size balls, and then dip into the melted milk chocolate coating, using a fork to let the excess chocolate drip off.
Color the decorators sugar with a small amount of green food coloring and sprinkle on top of the truffles.