what colour is blood
The idea that oxygenated blood is red and deoxygenated blood is blue is a common misconception. In fact, human blood is never blue. It does change color depending on the level of oxygenation. In the arteries, where blood is fully oxygenated, it appears bright red, while in the veins, where the oxygen is depleted, it is a dark red. Blood derives its red color from hemoglobin, a reddish iron-containing protein that is found in red blood cells.
Vertebrate blood is bright red when its haemoglobin is oxygenated and dark red when it is deoxygenated. Some animals, such as crustaceans and mollusks, use hemocyanin to carry oxygen, instead of hemoglobin. Insects and some mollusks use a fluid called hemolymph instead of blood, the difference being that hemolymph is not contained in a closed circulatory system.