In the 1260s and 1270s the glaziers, responding to a wider trend, began to employ large quantities of the silvery-grey glass known as grisaille.  Set in this field are broadly-depicted, brightly-colored monumental figures.  Such a combination, lending greater legibility, was particularly suited to the upper windows of the choir where brilliant luminosity accompanies the enhanced sanctity of the space.  The color palette changed with increasing use of yellow, green and purple.  Surviving panels include the monumental images of bishops and Apostles