As sweaters go, it was pretty unattractive: a black-and-white acrylic cardigan. But to photographer Stephen Mosher, who plunked down $30 for the thing in 1985, it was more than Mr. Rogers chic—it was, he says, a "canvas." Struck by the garment's ability to bring out the wearer's true colors, Mosher, 39, spent five years haunting stage doors and writing letters, coaxing hundreds of celebrities to pose with the sweater. "The sweater is the same," he says, "but the personalities are so different." The resulting coffee-table tome—with proceeds benefiting several AIDS charities—is The Sweater Book—Hundreds of People...One Common Thread, a collection of 522 photos, including one of Sarah Jessica Parker and Matthew Broderick, who slipped into the sweater in 1995 (they were "so into each other," says Mosher), and a goofy Whoopi Goldberg ("she put it on and did her thing"). Meanwhile, the sweater's days of cozying up to the A-list are long gone: Mosher lost it back in 1998.