Considered dark meat as it is darker than leaner breasts because leg muscles are used more and hence have more myoglobin proteins, which help ship oxygen to muscle cells and are highly pigmented.
When red or dark meat is cooked, the myoglobin's color changes depending on what the meat's interior temperature is. Above 140° F (60° C), myoglobin loses its ability to bind oxygen, the iron atom at the center of its molecular structure loses an electron, and a tan-colored compound called hemichrome is formed, giving medium-done meat its color. When the interior of the meat reaches 170° F, hemichrome levels rise, and the myoglobin becomes metmyoglobin, which gives well-done meat its brown-gray shade.
When cooking turkey: above 145°F, white meat begins to dry out. Dark meat, with its connective tissue, on the other hand, has to be cooked to at least 165°F