This thesis re-approaches medieval literature in terms of its investment in visuality in general and chromatic perception in particular. The introduction raises the philosophical problem off-colour: its status as an object for science, role in perception, and relationship to language and meaning as expressed within inter-subjective evaluation. Two modes of discourse for colour studies of medieval literature are proposed: the phenomenological (from the philosophical tradition of such as Maurice Merleau-Ponty) seeking localised networks and patterns of inter-subjective, embodied, perceptual meanings and values; and linguistic (informed by the philosophical psychology and language philosophy of Ludwig Wittgenstein), focusing on the lexicalisation of colour experience and creation of semantic distinctions corresponding with changing colour concepts, which in turn shape individual perceptions (both first-hand experience and that of reading). Part One introduces key medieval ideas and theories pertaining to visual perception in general, and chromatic perception in particular. The authority for, and influence on medieval writers of Plato's Timaeus, Aristotle's De Anima and Parva Naturalia, and relevant biblical material is considered. Subsequent chapters explore Patristic and Neo-Platonist developments in extramissive thought, locating within this tradition the roots of a synthesis of natural philosophy with Christian theology that is found in later medieval thought and its dealings with perception and colour. A key movement in the theology of light in relation to colour is connected to the wider philosophical movement from largely "extramissive" to largely "intromissive" models of perception. This shift in theory and its significance for colour perception is explained in terms of the impact of Aristotle's material colour theory as found in De anima and the De sensti et sensato section of his Parva Naturalia from the late twelfth century onwards. The part concludes with a detailed study of the nineteenth chapter of Bartholomaeus Anglicus's thirteenth-century encyclopedia, De Proprietatibus Rerum, which provides access to an important range of ideas and sources relevant for accessing the medieval mind in its intellectualized perception of colour. Lastly, such philosophical and theological sources and ideas as are found in Part One are compared with relevant examples from literary texts, ranging from the Middle English poem, The Parliament of the Three Ages, to Christine de Pisan's Le Livre de la Cite des Dames. Part Two treats colour perception in relation to a particular medieval phenomenon: the rise of medieval heraldry and the armorial function of the herald. It considers the spiritual and secular ideologies of chivalry and their relationship to armorial displays as found portrayed and construed in various genres of chivalric literature. Texts under discussion include books of chivalry and arms from the early thirteenth to fourteenth centuries, such as those principally indebted to New Testament armorial allegory and motif (from writers such as Ramon Llull to Geoffrey de Charny), to later fourteenth-century treatises employing Aristotleβs De sensu et sensato to establish a secular hierarchy of chivalric colours. The study culminates with Part Three, offering responses to and discussions of particular medieval fictions in terms of their phenomenological, linguistic and intertextual treatment of colour perception. Medieval texts addressed include, amongst others, Le Roman de la Rose by Guillaume de Lorris and Jean de Meun, and four Middle English metrical romances: Sir Gowther, Sir Amadace, Sir Launfal and Sir Gawain and the Green Knight