The most common colors are brindle, then fawn, with pieds being less common than the other colors. The breed clubs do not recognize any other colors or patterns. This is because some colors come linked with genetic health problems not usually found in the breed. These include blue coloration, which is linked with a form of alopecia (hair loss or baldness), sometimes known as 'Blue Dog Alopecia'. Although this is heavily disputed by some organizations, it has been suggested that the health, hair and skin conditions are caused by the color pigment (melanin) clumping in the hair shaft itself. Even dogs that are not blue can develop 'blue dog alopecia' or canine follicular dysplasia.