The former Dawson's Creek star unveiled her subtle change at the Jingle Bell Ball at Madison Square Garden in New York over the weekend.
Katie's locks always look in fab condition so it's probably no surprise to learn she's an ambassador for Alterna Haircare, a company specialising in natural, organic products.
At the weekend's festive concert, Katie went for a fun and flirty look at the event, teaming a very short black skater skirt with a studded white jumper featuring a peep hole design.
She's just back in the US after filming new movie The Giver in South Africa and has been seen out and about in freezing New York in recent days doing the school run with seven-year-old daughter Suri Cruise.
Suri didn't join her on the red carpet for the Jingle Bell Ball but with a lineup including Ariana Grande, we wonder if she was waiting in the wings?