The Colour of Veins

When blood is observed under normal light (visible white light), it appears to be red. This is because oxy-haemoglobin only reflects the red light back into our eyes. All other colours of light are absorbed by the blood, meaning we can only see the red pigment under normal conditions. The skin absorbs low frequency wavelengths of light including the colour red, therefore the colour changes from a deep red to a blue as these are the only frequencies that can penetrate and reflect through the fat. This light is also affected by the presence of yellow subcutaneous fat (beneath the skin), changing the pigment to a green colour. The exact colour is also affected by the concentrations of Oxygen and Carbon dioxide. Oxygen increases the reflected red light, whereas diffused Carbon Dioxide increases the reflected blue light. Veins are largely translucent meaning that any observed colour change is mainly due to the colour of the dark venous blood, the depth of the vein and the surrounding tissues. Veins are often more visible than arteries as they are more commonly found close to the surface of the skin. This is largely due to one of their primary functions; to act as a cooling system within the body (heat exchange). Deep veins pump deoxygenated blood into the superficial veins to facilitate heat transfer during periods of intense exercise or activity. Arteries are located deeper within muscular tissue to prevent injury.
If a blood vessel containing higher quantities of Carbon Dioxide is located close to the surface of the