Some of these include black tricolor (black/tan/white), liver and white, and red tricolor (red/tan/white) which have also been seen regularly, and other colours such as blue, lilac, red merle, blue merle, brindle, and Australian red (also known as ee red, blonde, recessive red, or gold) which is seen less frequently. Some border collies may also have single-color coats. Eye color varies from brown to blue, and occasionally eyes of differing color occur; this is usually seen with merles. The ears of the border collie are also variable — some have fully erect ears, some fully dropped ears, and others semi-erect ears (similar to those of the rough collie). Although working border collie handlers sometimes have superstitions about the appearance of their dogs (handlers may avoid mostly white dogs due to the unfounded idea that sheep will not respect a white or almost all white dog), in general, the American Border Collie Association considers a dog's appearance to be irrelevant.