Q. 1. What is the Mantelletta used for?

A. 1. The mantelletta, an Italian diminutive of Latin mantellum 'mantle', is a sleeveless, knee-length, vest-like garment, open in front, with slits instead of sleeves on the sides, fastened at the neck, once even more common than the mozzetta.

The mantelletta, which was formerly worn by all bishops and some of the monsignori, is now only used by the seven protonotaries apostolic de numero.

The colour for cardinals was ordinarily red, in penitential seasons and for times of mourning it was violet, on Gaudete and Laetare Sundays rose-colour; for the other dignitaries, the same distinctions being made, the colour was violet or black with a violet border. Cardinals and bishops belonging to orders which have a distinctive dress, also abbots who are entitled to wear the mantelletta, retain for it the colour of the habit of the order (gray for Franciscans, black for Dominicans, white for Cistercians, etc.). The vestment was made of silk only when it is worn by cardinals or by bishops or prelates belonging to the papal court.

Under reforms enacted by Pope Paul VI and specified by an instruction of the Secretariat of State in 1969, the mantelletta was abolished for cardinals and bishops, who now wear the mozzetta when appropriate. The violet mantelletta is no longer used except by a handful of prelates who reside in Rome, primarily the seven remaining apostolic protonotaries de numero and a few superior prelates of the offices of the Roman Curia if they are not bishops. It is now effectively a garment of the diocese of Rome; other monsignors do not use it. According to Noonan, the proper color of the mantelletta for chapters of canons who still wear it is grey or black with colored trim.

[Source: https://en.wikipedia.org/wiki/Mantelletta]