Liver is a term used to describe certain types of dark brown color in dogs and horses.
In dogs, It is a dark brown grayish chocolate shade.
In horses, "liver chestnut" is a term used to describe a chocolate-colored chestnut horse. A liver chestnut is the same genetically as a regular chestnut, but the shade is a dark brown rather than the reddish or rust color more typical of chestnut. A horse that appears to be a liver chestnut but has a light colored mane and tail, sometimes colloquially called a "chocolate palomino," could be a horse manifesting the champagne gene. However, "flaxen" or light-colored manes and tails are also seen in chestnuts.