Blake Lively has gone from bright blonde to saucy redhead overnight, surprising onlookers at the Time 100 Most Influential People party in New York.

The Gossip Girl star, known for her signature long blonde locks, offset her new-look tresses with a stunning aqua gown by Zuhair Murad, drawing comparisons to Ariel from The Little Mermaid.

There's no word yet on whether the new colour is for a role - Lively went from blonde to brunette recently for her stint in the Green Lantern in an effort to "emulate" her character – but it certainly makes for a change to Lively's self-confessed "low effort" hairstyle.

"My hair is mostly natural," explains Lively. "The colour gets touched up every six months, and the "unraveling curls" are created not with fancy techniques and curling irons, but by letting my hair dry in a simple chignon.