The Colour of Blood

What’s the colour of blood? Is your answer Red?

Well, red is not the only blood colour available – there is a whole rainbow out there.

Blood also comes in blue, green, violet, and even colorless varieties. All this is because different organisms have different proteins. The coloring matter of blood (hemo-chrome) is largely due to the protein in the blood, responsible for oxygen transport.

Let’s explore the Colors

Raging Red- Humans and majority of other vertebrates have Haemoglobin – an iron containing protein, which imparts the red color to the blood. Haemoglobin is the respiratory pigment that plays a vital role in ferrying oxygen around the body to your cells and helping carbon dioxide back to the lungs where it can be exhaled. The iron in the protein is responsible for the red tinge.

The spectrum of light absorbed by hemoglobin differs between the oxygenated and deoxygenated states. The arterial blood and capillary blood are bright red, as oxygen imparts a strong red color to the heme group. Deoxygenated blood is a darker shade of red; this is present in veins, and can be seen during blood donation and when venous blood samples are taken.

Our blood in veins appears blue because of the light-scattering properties of the skin and the interaction of light with both the blood and the skin and tissue covering the veins. But the actual color of the blood (human and some vertebrates blood) is always red.

Bleeding blue - Crustaceans, spiders, squid, octopuses, and some molluscs all have blue blood as they have the protein - Haemocyanin . The differing structure of the pigment, as well as the incorporation of copper atoms instead of iron, leads to the blood being colourless when deoxygenated, and blue when oxygenated.

Going Green - The blood of most annelid and some species of worms and some marine polychaetes use chlorocruorin to transport oxygen that imparts green colour to their blood. The skink, however, seems to have high levels of biliverdin in its blood, which also gives the blood a green color.

Paint it purple - In a limited range of marine worms, marine invertebrates sipunculids, priapulids, and brachiopods. The purple colour is caused by yet another different respiratory pigment, this time one called haemoerythrin.

So next time if someone asks you what the color of blood is. Instead of saying red, ask them whose blood they are talking about?