COLOR FORMS: Christie’s will today auction a series of fashion illustrations by the late René Gruau of dresses by Dior, Balenciaga, Castillo for Lanvin and others. The 20 illustrations, many of which date from 1950, were commissioned by Fleur Cowles for her magazines Look and Flair, and later hung on the walls of her home. They will be sold as part of a 20th Century Decorative Art & Design auction at Christie’s King Street in London. The bulk of the illustrations are gouache on paper, although there are some oil paintings, and the estimates range from 1,500 pounds, or $2,400, to 10,000 pounds, or $16,000. Christie’s holds the world record for Gruau’s work: In 2010, it sold “Reverie,” an oil on canvas of a ballgown-clad woman flopped on a sofa, for $218,500.