J. W. Root was one of the main figures in the history of Chicago architecture. This paper by Valentino Danilo Matteis explores his theories on a colouristic approach towards building, and his extensive understanding of the contemporary debate in art and architecture through the example of his masterpiece, the Monadnock, a rather misunderstood building that condensed many of the architect’s ideas, but was deprived of others, above all its -and Root’s- astonishing sense of colour.