Blue and gold: the gold represents the wheat fields. The blue has changed shades multiple times over the years, ranging from navy to royal, and represents the blue skies. These colors are mentioned in the Whitman hymn.
The Whitman College colors were adopted officially in 1893, along with an unofficial college yell. The Collegian says in February, 1893:
The question of college colors has long been agitating the minds of the students. When the football team ordered suits, they found it necessary to choose at once, and with the concurrence of the Athletic Association, they decided that the college baseball and football teams and their friends should be known by their Blue and Gold. They chose, we think, not without aesthetic taste, considering our Blue Mountains and golden fields.