The American bulldog is a stocky, well built, strong-looking dog, with a large head and a muscular build. Its coat is short and generally smooth. The breed is a light to moderate shedder; however, they should be brushed on regular basis. Colors, while historically predominantly white with patches of red, black, or brindle, have grown in recent years to include many color patterns including black, red, brown, fawn, and all shades of brindle. The color conformation is quite varied, but solid black or any degree of merle is considered a cosmetic fault, and a blue color is a disqualification by the NKC Breed Standard. Black pigmentation on the nose and eye rims is preferred, with only some pink allowed. Eye color is usually brown, but heterochromia also occurs, although considered a cosmetic fault. American Bulldogs can be droolers; this varies and is more prevalent in the Bully type, which is generally a larger, heavier dog with a shorter muzzle. Standard or Performance types are generally more athletic with longer muzzles and a more square head. It is important to note that many modern American Bulldogs are a combination of the two types usually termed hybrid. In general, American Bulldogs weigh between 27 to 54 kg (60 to 120 lb) and are 52 to 70 cm (20 to 28 in) at the withers, but have been known to greatly exceed these dimensions, especially in the out of standard, nonworking stock.