all served as executive producers throughout the course of the series. In subsequent seasons, Steve Mulholland, Kent Hodder, Nancy Bordson, James D. Parriott, and Peter Horton have also been executive producers, with Allan Heinberg joining the show in 2006 in this role. As of season eight, the executive producers were Rhimes, Beers, Gordon, Vernoff, Corn, Wilding, and Heinberg. Rhimes is the series head writer, or its most prolific writer. She often promotes the show by answering fan questions on her Twitter account. Other members of the writing staff are Vernoff, Wilding, Peter Nowalk, Stacy McKee, William Harper, Zoanne Clack, Tony Phelan, Joan Rater, and Debora Cahn. From the second through seventh seasons, the writers maintained a blog entitled Grey Matter, where the writer of an episode discussed background of the writing. Directors vary by episode, with Rob Corn directing most frequently, followed by Tom Verica. Horton, Edward Ornelas, and Jessica Yu have also directed a substantial number of episodes. Cast members Chandra Wilson, Debbie Allen, and Kevin McKidd have each directed multiple episodes. Grey's Anatomy has been edited by Susan Vaill since the show's inception, and David Greenspan was named an editor in 2006. Casting directors Linda Lowy and John Brace have been a part of the production team since 2005. The production design is led by Donald Lee Harris, assisted by art director Brian Harms, and costume design is led by Mimi Melgaard. Working alongside Melgaard, Thomas Houchins supervises costumes, Ellen Vieira is the makeup artist, and Jerilynn Stevens serves as a hairstylist. The Director of Photography is Herbert Davis. The music coordinator is Danny Lux. Karen Lisa Pike, M.D. is the on-set medical consultant, alongside Linda Klein, an RN. In an interview, Ellen Pompeo (Meredith Grey) stated "We always ask Linda, you know, what is this procedure, what is this surgery, when is this performed, what happens"- various members of the cast spoke of the importance of having real surgeons around especially in learning how to properly hold instruments, how to accurately use medical language and develop their characters in an authentic way; most of the cast members observed real surgery in real life as preparation for their roles. The production staff is part of a Grey's Anatomy softball team that competes against other television shows, such as CSI: Crime Scene Investigation. Casting Grey's Anatomy used a color-blind casting technique, resulting in a racially diverse ensemble. Each role