Only a small portion of the blood is red. The red blood cells are responsible for the colour.
They carry an iron-containing protein molecule called haemoglobin. The iron it contains binds oxygen, giving blood its typical colour.
Blood through veins appears blue through the skin, and that is because of how light travels through the skin.
Similar to people, most animals also have red blood.
However, there are a few exceptions. Some types of octopus, squid and crustaceans have blue blood because of the high concentration of copper.
When copper mixes with oxygen, it gives their blood its blue colour.
Some animals bleed green. The skink, which is a type of lizard, has green blood, which is due to by-products of the liver.
As humans, we excrete to remove waste but for these lizards, it builds up in their bodies, making their blood green.