Thus, when two Shih Tzu mate, there is a possibility that their offspring's coat will be similar to the sire's color, dam's color, tricolor, or a mix of both parents' color in one classification. An interesting point (and often a point of confusion) is that while the coat color of those with black pigmented skin (nose, lips, pads, also referred to as 'leather') is determined by the color of the coat itself; the coat color on dogs with either liver or blue pigment is categorized by the color of the pigment. Thus, a parti colored (white and another shade) Shih Tzu with blue pigment is a 'blue and white' regardless of the tint of the hair which might very well appear similar to a gold and white or other colors. It usually affects middle-aged dogs and is seen in all breeds.