Listeners who picked up Ember Records’ 1970 LP Future Star Explosion – New Faces of the ’70s might have been beguiled by the third track on the second side. The lightly psychedelic “Sunshine in My Rainy Day Mind” introduced the captivatingly ethereal voice of singer Polly Niles. Yet those looking for more of Niles, a New York-born, conservatory-trained performer, would have been disappointed. “Sunshine” remained her only released track for decades, until labels in the CD era began mining the Ember vaults for lost gems. Soon, her renditions of familiar songs like…