The English Kennel Club describes three different colors: 'tricolor, blue merle, and sable (ranging from golden through mahogany), marked with varying amounts of white and/or tan.' Essentially, however, a blue merle dog is a genetically black dog, either black, white, and tan (tricolor). In the show ring, blue merles may have blue eyes; all other colors must have brown eyes. The two basic forms of inherited eye diseases/defects in Shelties are Collie eye anomaly (CEA) and progressive retinal atrophy (PRA).