Hilary Duff's Aqua Hair
Credit: Jim Spellman/WireImage

Hilary Duff is officially Lizzie McGuire no more. The star is back on the scene with a hot bikini-ready bod, freshly colored strands, and a new show—Younger, a series in which she plays friend and co-worker to Sutton Foster's character, a 40-year-old mom who pretends she's 26. But did her new project have anything to do with her recent dye job? Is the mom to 3-year-old Luca, in fact, channeling a younger spirit?

"I was just ready to do something a little bit different. I've dip-dyed my hair at the bottoms before, but I really wanted to go for it," Duff tells InStyle at the Younger premiere on Wednesday. "I was vacationing in Cabo, Mexico, and I was like, 'I can have blue hair, why not?'"

And what did her son think of her pastel tresses?

"He saw me and he was like, are you a mermaid, mom? Are you a mermaid?" she says while laughing. "Before it was a little more green and now it’s a little more blue, so he was like: 'Is green? Is blue?' He's so funny because he could not figure out what color it was. He doesn’t have aqua in his repertoire yet, so it was adorable."

The star stepped out for the Younger premiere and unexpectedly complemented her aqua waves with a sexy plunging red-hot number that she color-matched with a fiery lip—Dior Rouge lipstick in Blazing Red 638 (limited edition, try Royale, $35; And while she pulled off the surprising color combo like a pro, she confessed that it's been more of a challenge in terms of fashion and beauty. "It's harder now—colors that I wore before or ways I did my makeup don't always work now," she admits. "It happens to work with red and with some bold colors, but I've been keeping it a lot simpler with whites and blacks."

Coincidentally, Duff wasn't the only Younger star to get in on some #YOLO action. Her co-star Nico Tortorella also underwent a color change that resulted in an amazing twinning moment that he insists was a complete accident.

"I knew she dyed her hair green two weeks ago, and I was like, I’m going to dye my hair blue," Tortorella explains. "In between those two colors fading, it was just coincidence that yesterday, it was exactly the same color, so I switched it again last night."

At the premiere, he debuted a head of Kelly green that he jokes was the result from "drinking way too much wheatgrass." In all seriousness though, he described his hair as "forest-green emerald," saying, "I'm basically the Joker, let's be honest."