A few of Hollywood’s biggest names have more than fame in common: hairstylist Justine Marjan (@justinemarjan), who’s responsible for styling their manes. Marjan started as an assistant to Jen Atkin, and has built an empire of her own, counting celebrities like Olivia Culpo, Khloe Kardashian and Ashley Graham as regular clients—talk about a glow up. American Salon sat down with Marjan to get the dish on her best advice, her …