Photographers caught the 34-year-old actress walking around the park, dressed casually in a t-shirt and leather jacket, and hiding her new hair color under a cap.
McAdams split with Welsh actor Michael Sheen, her boyfriend of two years, back in February. The pair met on the set of Woody Allen's film "Midnight in Paris."
McAdams has experimented with hair dye before. Click through the photos above to check out previous shades.