There is a new historical fiction book that is about Charles Rennie Mackintosh, a young friend, and World War I in Britain. It's written by Esther Freud, Lucian Freud's daughter and Sigmund's great granddaughter. (I always have to be careful when I type Freud, otherwise I make a freudian slip and type it as Frued, which I would pronounce "frood.")
Mackintosh was one of the main artists in the arts and crafts and the art nouveau movements. He was an architect and a painter. Of particular interest to watercolorists is that he painted many exquisite flowers in watercolor. One of these graces the cover of the novel.
NPR has a review of the novel and an interview with the author: http://www.npr.org/2015/01/24/379131030/two-outcasts-form-an-artistic-bond-in-mr-mac-and-me
There are quite a few art books available on Mackintosh, some that focus on his flower paintings.