Reduced hemoglobin is the old name before, but now it is mostly called deoxygenated hemoglobin, which refers to hemoglobin that does not carry oxygen. Reduced hemoglobin is purple-blue in color, and the average concentration of reduced hemoglobin is 2g/dl in normal capillaries. When reduced hemoglobin reaches 5g/dl in capillaries, the skin and mucous membranes are cyanotic, called cyanosis, which is common in hypoxic hypoxia. When reduced hemoglobin rises to 5g/dl of blood, the blood becomes dark purple. Venous blood is dark red because it contains more reduced hemoglobin, and it is cyanotic through the skin. The veins on the arms, which are generally called cyan veins, are cyan because they are not able to carry oxygen and carry less oxygen, so they are in a cyan-purple vascular state. This is the explanation of reduced hemoglobin.