Colour is not just a pigment. Each colour has always had a symbolic meaning, different in different epochs and cultures.
White is associated to symbols of purity as the lily and the dove.
Starting from the 9th century, black, the colour of humility and penitence has become the colour of ecclesiastical robes. Afterwards, black will become the colour of elegant and expensive clothes worn by kings, princes and noblemen. It will remain fashionable until mid-17th century.