A merle Chihuahua is a Chihuahua with a dappled coat. Merle is a coat pattern found in many domestic dog breeds; it consists of darker blotches of color on a lighter background of the same hue.
In Chihuahuas, merle is strongly associated with a host of health problems. It is linked to deafness and abnormalities of the eye, skull and reproductive system. Several countries, including all 83 countries that use the FCI European standards, ban merle Chihuahuas from being registered in an effort to prevent further breeding. As of 2014, the American Kennel Club accepts any coat or pattern in show-quality Chihuahuas, including merle.