I do know that in 1888, bishops were given the right to a purple biretta (not sure as to when magenta purple came into vogue). Before Vat 2, prelates of religious orders each had a distinctive mode of dress that included a mix of pontifical items added to their standard habits. This usually included a zuchetto, biretta, ring and pectoral cross. If the order used a fashia, then a pontifical one replaced it. Before Vat 2, auxiliary bishops did not wear a mozetta. These bishops dressed as prleates di mantelleta, except they included the violet zuchetto and biretta, cross and ring. Just as today, they did not have the right to a croizer. After Vat 2, ALL bishops, temporal or regular, auxuliary or co-adjutor, dress the same as the ordinary. A few regular bishops do opt for their habits plus the correct zuchetto, cross and ring, and maybe the sash.