Out of the Blue has refined the art form of 4-part a cappella (unaccompanied) harmony in the barbershop style, and are members of Sweet Adelines International. Sweet Adelines International is a worldwide organisation whose mission is to advance the art form of 4-part a cappella harmony through education, performance and competition. There are 30,000 members worldwide. Barbershop had its humble beginnings in the deep south of America , but has been transformed into a modern and exciting art form of singing and performance.