Color of the Meat

The color of the meat depends mainly on the amount of protein called "myoglobin" it contains within. This protein is present in all muscle, including meat and stores oxygen in cells. It receives oxygen from another protein known as "hemoglobin" whose function is to transport oxygen from the lungs to the cells throughout the body.

Darker meats  contain more myoglobin.

The amount of myoglobin present in meat also increases with age of the animal. Veal from very young cattle can have as little as 2 mg of myoglobin per gram of meat, while beef from old cattle can have as much as 18 mg/g. Looking at the above table we can see that poultry meat is much lower in myoglobin and this is the reason why it is much lighter in color than other meats.

Why Are White and Dark Meat of Poultry Different Colors?

The pink, red, or white coloration of meat is due primarily to oxygen-storing myoglobin which is located in the muscle cells and retains the oxygen brought by the blood until the cells need it. To some extent, oxygen use can be related to the bird's general level of activity: muscles that are exercised frequently and strenuously--such as the legs--need more oxygen, and they have a greater storage capacity than muscles needing little oxygen. Turkeys do a lot of standing around, but little if any flying, so their wing and breast muscles are white; their legs, dark.

Chickens spend a lot of time standing around. Their thigh and leg muscles are used constantly, and so the meat from these parts is dark. Chickens rarely fly, and then only for very short distances, the meat that comes from the breast and wings is white. Wild birds such as ducks fly a lot; the meat from their breasts and wings is dark.

Fish float in water and don't need constant muscle energy to support their skeletons. Most fish meat is white, with some red meat around the fins and tail, which are used for swimming. Most of the fish don't have myoglobin at all. There are some antarctic cold water fish that have myoglobin but it is confined to the hearts only (flesh of the fish remains white but the heart is of the rosy color. The red color of some fish, such as salmon and trout, is due to astaxanthin, a naturally occurring pigment in the crustaceans they eat.