What are different colors of blood in animals?

Blood color in animals varies primarily due to the type of respiratory pigment present. Most vertebrates, including humans, have red blood due to hemoglobin, which contains iron. Insects and some crustaceans have blue blood because their hemolymph contains hemocyanin, which uses copper for oxygen transport. Other variations include green blood in some worms and leeches due to chlorocruorin, and purple blood in certain species of octopus, which also rely on hemocyanin.