When Rebecca Romijn decided to lighten up her hair recently, she wanted the color to be strong, but subtle.

“I don’t change my look much, because I’m a mom, and on a day-to-day basis I have to be as low-maintenance as possible,” she tells PEOPLE. “But heading into red carpet season, you have to figure out how to make your hair look as great as possible, as often as possible.”

Rebecca Romijn only has 30 more days to go before she's officially over the hill. The actress and supermodel, 39, spoke to Us Weekly about the milestone birthday during the Third Annual Veuve Clicquot Polo Classic in L.A.'s Pacific Palisades October 6.

"It's funny: All year long I kept saying, 'I think I want to do a really big party,' and the closer you get to it, I don't really feel like celebrating," the Ugly Betty alum said. "I loved my thirties! It's not like I'm not looking forward to 40; I'm just sad to be leaving my thirties."

Rebecca Romijn is best known as Mystique in the X-Men films and Alexis Meade on television's Ugly Betty. This Friday she takes the plunge into musical theater when she steps onto the stage as Swedish bombshell Ulla in The Producers at The Hollywood Bowl, joining Broadway veterans Richard Kind, Jesse Tyler Ferguson, Roger Bart and Gary Beach.