Ask 16-year old Katherine Heigl, who did just that for Steven Seagal in Under Siege 2: Dark Territory. To play Seagal's character's niece, Heigl had her hair dyed from its natural blond, seen last year in My Father, The Hero, to jet-black. "It was really dark," she says. "Now I'm keeping it brown with a vegetable dye."

But there are some authorities that supersede even a blockbuster action-movie hero. For instance, Heigl's mom. "Steven set me up with a personal trainer to lose 10 pounds and get some narrowness to my face," says Heigl, already very thin at 5 feet, 8 inches, and 115 pounds. "But after I'd lost 6, my mother said, 'No more.'"

Common teenage crises, though, must be handled alone. "The atmosphere in the weight room can be really competitive," the Connecticut resident says. "If you get on the StairMaster after someone did 20 minutes, you feel like you have to do 40." Then there's the between-period stop in the girls' bathroom to check her makeup: black mascara, light-pink blush and lipstick. "I feel kind of vain when I go by myself," she admits. "But it's high school. You have to look good." Even Steven Seagal can't protect you from peer pressure.