Sheets of parchment dyed or painted purple, as a background for illumination or for script in gold or silver (see Chrysography). Purple pages were introduced into high-grade book production during the Late Antique and Early Christian periods as marks of costliness and luxury and sometimes to imbue a work with imperial connotations (from the Greek porphyrogenitus, or 'born in the purple', used of children born to reigning Byzantine emperors). Several important liturgical volumes made in the Insular, Anglo-Saxon, Carolingian, and Ottonian worlds employed purple pages, and they enjoyed a revival during the Renaissance. In Mediterranean regions, murex purple (a shell-fish dye) was often used, but in northwestern Europe alternatives such as the plant-dye folium (from the turnsole, or crozophora tinctoria) seem to have been more frequently employed.
Michelle Brown, Understanding Illuminated Manuscripts (Malibu, CA: J. Paul Getty Museum in association with the British Library, c1994).