Katherine Heigl Goes Brunette

Credit: Jean Baptiste Lacroix/WireImage.com

Bye, bye, blonde!

Katherine Heigl showed off brunette locks during an outing Monday in Los Feliz, Calif.

The reason for the new look?

The actress, 31, hasn't said.

She recently returned to the set of Grey’s Anatomy (after taking a three-month maternity leave after adopting daughter Naleigh last year with husband Josh Kelley).

After that, her future on the show remains to be seen.

Heigl -- who will receive the ShoWest award for Female Star of the Year in Las Vegas later this month -- has four films in development and will release two movies, Killers and Life As We Know It, later this year.