Monday evening's CFDA Awards were a big deal for the Row's Mary-Kate Olsen, who, along with her twin sister Ashley, received the award for Womenswear Designer of the Year. But the diminutive former child actress is making headlines for other reasons as well: She's gone brunette.

[Picture] Olsen, 25, paired her black self-designed gown with stick-straight chocolate locks at the event, prompting RadarOnline to speculate that she's trying to look more grown-up for her rumored new beau, 42-year-old Olivier Sarkozy. Given how aggressively mature some of Mary-Kate's previous looks have been (see: turbans, vintage cloaks, near-white dye jobs), it's unlikely this is the case.

The Olsens edged out Marc Jacobs and Proenza Schouler for their big win. According to NYMag, Ashley petted her sister's new 'do during their acceptance speech.