Is Blood Blue Before It Hits Oxygen?

Blood is blue or red depending on it having combined with oxygen. The blood in the arteries (blood vessels that carry blood away from the heart) is red because oxygen has attached to the hemoglobin (a pigment that combines with oxygen) in the red blood cells. The blood in the veins (blood vessels that carry blood from the body cells back to the heart) is blue because the hemoglobin in them is not combined with oxygen. When blood from the vein is exposed to air, it does turn red due to combining with the oxygen present in the air.