Known for their folky-electric sound and diehard fans, Emily Saliers and Amy Ray move into uncharted territory with INDIGO GIRLS PROJECT, a collaboration between the duo and the Atlanta Ballet. The Indigo Girls appear live OCT. 18-21 to accompany Margo Sappington's choreography. Also featured: George Ballanchine's neoclassic Serenade set to Tchaikovsky's Serenade in C Major for String and Orchestra. $20-$60. Thurs. 7:30 p.m.; Fri. 8 p.m.; Sat. 2 and 8 p.m.; Sun. 2 and 7 p.m. Fox Theatre, 660 Peachtree St. 404-817-8700. www.atlantaballet.com.