"the great chord of perfect colour"

In The Gutenberg Galaxy (1962), in the final section, "The Galaxy Reconfigured of the Plight of Mass Man in an Individualist Society", Marshall McLuhan quotes 19th century critic John Ruskin as he speaks of his desire

to revive the art of illumination…of making writing, simple writing, beautiful to the eye, by investing it with the great chord of perfect colour, blue, purple, scarlet, white, and gold, and in that chord of colour, permitting the continual play of the fancy of the writer in every species of grotesque imagination….