The actress, who turns 35 this month, showed off a dark chocolate brown, shoulder length 'do as she attended the Z100 Jingle Ball in New York last weekend.
The transformation was subtle, but Katie's new colour is strikingly similar to Kate Middleton's new hair hue.
Clearly in the Christmas spirit at the festive concert, radiant Katie smiled widely for the cameras, wearing a studded white jumper and a short black skater skirt.
Katie was recently announced as haircare brand Alterna's co-owner and celebrity spokesperson. In a video she shot as part of their new campaign, Katie spoke about her different hairstyles over the years.
"I had this look for a long time, this was the look of Joey Potter," she said, referring to her Dawson's Creek character. "Easy, simple, straight-forward, girl-next-door – and it still works!"
Her most daring look was the chic bob that she debuted in 2008. "This was a big cut for me, doing a bob," she said. "I'd always wanted to have one and I enjoyed it."
Katie recently jetted back to the US after filming new movie The Giver in South Africa. She has been spotted doing the school run in New York with her seven-year-old daughter Suri.