GRACE POTTER On her solo set, the rocker is happy her pop roots are showing  Taking a sharp musical detour, Grace Potter—frontwoman for Grace Potter and the Nocturnals for more than a decade—has swapped her trademark jam-band sound for pop on her new solo album, Midnight. The change may seem drastic to fans of the Nocturnals’ rootsy rock, but understandable when you discover the pop classics that were among the staples Potter was raised on....