Georgia O'Keeffe mistrusted words. She claimed color as her language. Nevertheless, in the course of her long life, the great American painter wrote thousands of letters--more than two thousand survive between her and her husband, Alfred Stieglitz, alone. Jennifer Sinor's Letters Like the Day honors O'Keeffe, her modernist landscapes, and, crucially, the value of letter writing. In the painter's correspondence, we find an intimacy with words that...