The color of normal adult blood is dark red for venous blood and bright red for arterial blood because of the difference in oxygen content, with slight differences in color depending on the individual’s physique and underlying disease, as well as differences in the content of blood components: first, patients with anemia have relatively lighter blood color because of less hemoglobin, and the more severe the anemia, the lighter the color, but venous blood is still darker than arterial blood. Second, patients with high blood fat, blood color may appear milky white, especially venous blood is more inclined to milky white, because the veins are excreting waste, more fat in the blood. Third, patients with hypoxia, such as chronic obstructive pulmonary disease, gas poisoning and other hypoxic patients, because of the low content of oxygenated hemoglobin in the blood, the blood is dark red. Fourth, patients with food poisoning have a special color of blood, such as patients with nitrite poisoning have black blood color. Fifth, patients with hemolytic anemia or liver disease have relatively yellowish blood.