While some Popes have been buried in a white miter, the historical tradition has been for Popes to be buried in the orphreyed miter (mitra auriphrygiata), made of brilliant gold cloth with a band of gold trim for the border. Bishops wear this same gold cloth miter on many occasions including less solemn functions, for example during Advent and Lent.
Below is how Pius XII looked in 1958 atop the crimson bier in the Sala degli Svizzeri at Castel Gandolfo before the solemn procession of his corpse to Rome. Notice he was not buried in "la falda" (the white watered silk train attached to the back of the papal soutane that henceforth disappeared from papal funeral vestments). Pius XII was also the first deceased Pope not laid out in the Blessed Sacrament Chapel of St. Peter's. Instead, for the first time, his bier was placed in front of the main altar of St. Peter's to accommodate the massive crowds who came each day to see his mortal remains.
Below is how Pius IX looked when he was exhumed in 1956, found incorrupt, buried holding a crucifix, as was Pius XII and John XXIII. Images abound of recent popes being buried in red. The last pope to be buried was John Paul II in 2005, in red vestments, a white miter, and instead of holding a crucifix, a rosary was placed in his hands. The author of this article was privileged to have been there, and saw him lying in state in the Vatican Basilica every day before his final funeral Mass.