I make my own mmf but havd mixed results due to the climate. A good rule of thumb is twice as much icing sugar as marshmallow (in weight) and enough shortening to make it pliable and not stick to everything. Also a tablespoon of corn syrup in the marshmallow helps with pliability. I always add my coloring (americolor gel) to melted marshmallow before adding icing sugar to ensure deep vibrant colors. I’ve also had good results with black mmf using chocolate mmf recipe.