Mutton is definitely “red meat.” Red meat in culinary terminology refers to meat which is red-colored when raw, while in nutritional terminology, it refers to meat from mammals, and mutton is definitely red when raw and since it comes from sheep, definitely mammalian.
However, not all mammals provide strictly red meat. Veal is an example, as are certain cuts of pork, “the other white meat.” Poultry is divided between white meat (lower fat meat such as the breast) and dark meat. Most fish are definitely white meat, but there are bits of the tuna, for example, that are definitely red meat, in color, fat content, and taste. Here is one description:
“The exact definition of white meat varies by time, place, and culture, but domestic chicken and rabbit are invariably considered “white”, while the meat of adult mammals, such as beef, mutton, and horse is invariably considered “red”.
The meat of young mammals such as veal and milk-fed lamb, and that of pork is traditionally considered “white”; while the meat of duck and goose is considered “red”,though the demarcation line may be changing. Game is sometimes put in a separate category altogether (French viandes noires ‘black meats’).
A newer definition in the United States emphasizes not the appearance and strength of taste, but the fat content, making “white meat” synonymous with “lean meat”; traditionally “white” meats such as lamb and veal are reclassified as “red”. Sometimes, even fish and seafood, including fatty and dark-fleshed fishes such as salmon, mackerel, and tuna, may be considered “white meat”.”
( http://en.wikipedia.org/wiki/Red_meat )