It's very rare to find an aggressive or bad-tempered Newfoundland. One of the most important breed characteristics is its gentle, calm disposition. The dog's expression reflects its kindness and dignity--but don't let that fool you; Newfs can be big clowns too.
Physically the Newfoundland is a large, powerfully built dog. Overall the dog should give a deep-bodied, squarish appearance, with females having slightly longer bodies than males. The muzzle is short and heavy with a "soft" mouth, the eyes large and usually dark brown, the ears low and close to the head, and the head broad and slightly domed. Legs should be heavy and not too long, with rounded paws set straight on the legs. Toes are webbed. The tail should be thick at the base, heavily furred, and held low--the dog uses its tail as a rudder when swimming. The coat should be thick and glossy; the coat is water repellent, with a soft undercoat. Males stand about 28 inches at the withers and weigh around 150 pounds, females stand about 26 inches and weigh around 120 pounds.
There are four colors of Newfoundland. Solid black is very common, although it's not unusual for a black dog to have a few small white marks on the chest or toes. Landseer is the term for a black and white Newfoundland, named after Edwin Landseer whose famous painting, "A Distinguished Member of the Humane Society," depicts a black and white Newf. Shades of brown and gray are less common.