From Dante’s Inferno (4:130-131), meaning “master of those that know.”
"Vidi il Maestro di color che sanno | Seder tra filosofica famiglia" - "I saw the master of those that know, | seated amid the philosophic family"
Dante frequently acknowledges his debt to Aristotle whom he calls Maestro / Master and from whose writings and teachings Dante has based much of his works on.
http://goo.gl/tGq4OB
It is said that the play on the Italian use of ‘color’ and the English ‘colour’, is a connection that Joyce intended.
