This month’s Vogue cover features one of the most celebrated young actresses of today, Michelle Williams, channeling another famed blonde—the legendary Marilyn Monroe.

Williams, who portrays the screen siren in the upcoming movie, My Week with Marilyn, was shot for the cover by Annie Leibovitz, with hair by Oribe and makeup by Linda Cantello for Giorgio Armani Beauty. The hair color, in the spot-on shade of platinum that Marilyn was known for, was created by celeb colorist Anthony Palermo, color director of New York City’s Anthony Leonard Salon.

Getting the right shade of blonde took some research, says Palermo, who is known for doing blondes and who has worked with celebs like Maria Sharapova, Madonna and Scarlett Johansson, among others. “We needed lots of different references. We looked at lots of pictures from different eras, we investigated how she colored her hair,” he explains. “Then we did the color and compared it to Marilyn. We got it on point, but it takes exploration before you can call it the ‘Marilyn’ color.”

So how exactly did he achieve the Marilyn color? “I love the platinum colors by Wella,” says Palermo. “For this particular more modern New York Marilyn, I actually mixed a combination of Wella Color Charm toners, 1 part Royal Blonde and 1 part Nordic Blonde. These are a guarantee to get that perfect blonde bombshell…a.ka. Marilyn!” He first bleached the hair, then toned with a 20-volume developer. "The root color was purposely left in to look like a more modern version of Marilyn."

Williams, who had her hair colored on-site at his salon, has had the color since last year, adds Palermo. “She loves it. She’s a natural blonde to begin with, but to go extremely blonde, she loves it.” Though the platinum might be high-maintenance, it’s “totally worth it,” declares Palermo. “It’s traffic stopping, the ultimate bombshell. Everyone wants to look like [Marilyn]. For centuries to come, she will always be an icon and so will her platinum color.”