Ever since we first spotted Margot Robbie in the short-lived TV drama Pan Am, she's worn her signature shade of blonde -- worn it well, we might add! For her upcoming film Z for Zachariah, the Wolf of Wall Street star is swapping her typical glamorous look for a casual wardrobe and toned-down chestnut strands. "Prep for Z for Zachariah is well and truly underway," Robbie tweeted before posting a picture of her new hue. "I'm now officially a brunette, and spent the day milking cows and driving tractors!" Now that's what we call commitment to character! Combined with her casual getup, the tawny brown color is definitely a change, but we're convinced that the star can pull off just about anything -- her past red carpet looks serve as proof. Take a look at her new 'do after the jump, and see even more celebrity hair makeovers in our gallery!