Green isn't even one of ND's colors; can't they wear blue and gold?
Off-topic, I know, but if you want strange university colors, try Maryland. They have four: red, white, black, and gold. The flag is based on two heraldic shields, the first of the Calvert family, Lord Baltimore, and the second of the Crossland family, which was related. The city of Baltimore flies the black and gold shield as its flag. But the four colors of the two shields are what have led to the garish uniforms of the University of Maryland athletic teams.