From Muppet Wiki

The Tarnish Brothers are three Anything Muppets who have appeared several times on Sesame Street as back-up singers.

They first appeared in 1974, singing "I Just Adore Four" with Big Bird. In this appearance, the Tarnish Brothers consisted of one Pumpkin, one Fat Blue, and one Orange Gold Anything Muppet. All three had slick, black hair and thin mustaches, and wore the blue velvet tuxedos that they would wear in all their subsequent performances.

When the Tarnish Brothers appeared as back-up singers on "This Frog" and "Salida," the Orange Gold character had been dropped in favor a Lavender one. Aside from this change, however, their look stayed mostly the same. Their eyelids, however, which had all been purple in their first appearance, now matched the color of each character's skin.