What is the colour of blood inside the body?
Contrary to popular belief, the colour of blood inside the body, no matter how you look at it is red. Blood is bright red when oxygenated and dark red when it lacks oxygen. When you look at blood through your skin it may look blue, but that is the result of how colour wavelengths travel through and are reflected by the skin. To see a vein at all, light must pass through the skin and hit the blood in the vein. The blood then absorbs certain colours of light and reflects others back through the skin. In blood, longer, redder wavelengths can go more deeply into the skin than shorter, bluer wavelengths before being reflected. Therefore, a blood vessel below the skin looks blue because the blue light is reflected. In reality, blood is either dark or bright red, depending on the amount of oxygen. When blood passes through your lungs, oxygen surrounds the haemoglobin turning your blood bright red. Also when blood is exposed as in the air, like when you cut your finger, it turns bright red. Ho
