Something positive for Baltimore: Prince is throwing a "Rally 4 Peace" in Baltimore on Mother's Day, and he's asking everyone to wear the color gray in honor of Freddie Gray, whose death in police custody last month set off protests, riots and an overnight curfew in the city. Live Nation, the concert's promoter, said Tuesday that "several industry superstars" are expected to appear at the show at Royal Farms Arena, although it didn't name them.