The meaning of the coat colour of the dog reaches further than only to the field of breeding for beauty. Besides aspects of destination (hunting dogs, herding dogs) the clinical meaning is of particular interest. Some colours can show certain defects. Diseases of allowed colours are the colour dilution alopecia (CDA) in diluted (mostly "blue") pigmentation with its subtype of Black hair follicular dysplasia (BHFD) in black pigmentation and congenital deafness in extreme piebalds. Not allowed coat colours, which are connected with defects, are the extreme dapple of the Merle-syndrome and the "grey" Collie with cyclic hematopoesis.