The wearing of red papal shoes (then “sandals”) dates back to the earliest times of the Church. However, in 1566 St. Pope Pius V, a White Dominican, decided to change the papal vestments from red to white leaving only the Pope’s cappello (a wide circular brimmed hat), cape and shoes the color red. Usually elaborate, the leather soled, less structured papal “slippers” of the time were made of red satin and silk along with gold thread and embroidered ruby encrusted crosses.
Until the first half of the 20th century, it was customary for pilgrims having an audience with the Pope to kneel and kiss one of his slippers. Similar to many of noblemen of the time, the Pope also wore red slippers inside his residences and red Morocco leather shoes outside. Centuries later, Pope Paul VI decided to update his footwear and eventually discontinued the use of “slippers” altogether in favor of sturdy red shoes for both indoor and outdoor use.
Throughout Church history, the color red has been deliberately chosen to represent the blood of Catholic martyrs spilt through the centuries following in the footsteps of Christ. The red papal shoes are also linked to Christ’s own bloodied feet as he was prodded, whipped, and pushed along the Via Dolorosa on his way to his crucifixion, culminating in the piercing of his hands and feet on the cross. The red shoes also symbolize the submission of the Pope to the ultimate authority of Jesus Christ. Beyond this, it is said the red papal shoes also signify God’s burning love for humanity as exhibited during Pentecost when red vestments are worn to commemorate the decent of the Holy Spirit upon the apostles as tongues of fire rest upon their heads.
From: “Red Shoes and the Room of Tears” by Judy Keane http://catholicexchange.com/red-shoes-and-the-room-of-tears