When Sue Ellen Cooper turned 50 a few years ago, she decided she needed a jaunty red hat. Soon, she was buying red hats as birthday gifts for her friends, and together they formed the Red Hat Society (50-year-olds who possess a red hat, a purple outfit and a sense of joie de vivre are eligible for admission). Now there are more than 20,000 chapters nationwide, with a membership estimated at more than 400,000. That number is sure to grow with the publication of Cooper's new book, The Red Hat Society: Fun and Friendship After 50. Warner's first printing for the April 1 release was 72,000 copies; three weeks and seven trips to press later, the in-print figure is 230,000 copies. Cooper's first promotion stop was in Dallas for the annual Red Hat Society convention (April 14—18), followed by a 21-city, two-week book tour. The book recalls the genesis of the society and shares stories from members. It also talks about the Pink Hatters—younger women who are not old enough for the Red group but want to share in the fun. A Web site (www.redhatsociety.com) has information for women of all ages.