"Compte di Brazza," is a crisp white, completely double Parma with a strong perfume.  Parma violets are the most fragrant of the scented violets.  While they are perennial, they are tender and not winter hardy in most parts of the US so they should be potted and wintered indoors.   It is written that they will survive 20 degrees Fahrenheit, but not for long, and in my own experience, not at all.  I suggest Zones 7 (with protection) to 10.  To make the plants stronger and to produce more blooms, cut off the runners in late summer/early fall.  They will perfume an entire room, so the effort is worth it.