Baum, who has worked with the actress for nearly three years, tells Refinery29 that Johansson's red-carpet hair was a long time coming. "We've been growing out Scarlett's hair for a while now, and we've been gradually going blonde over the past eight months," she says. "It conveniently happens that we were in the home stretch of Scarlett's transition right before the red carpet." Baum's approach to going from brunette to blonde is slow and steady, and she touches up her famous client every 2-3 months. "I always tell my clients who transition to blond e to take it slow, and add colour and dimension as we go, and that's what we did with Scarlett."