How does de-oxygenated blood turn blue?

It is a common misconception that when blood lacks oxygen it turns blue. Probably, people draw this conclusion from the fact that when something like suffocating happens people's lips and complexion seem to turn blue-ish or purple due to lack of oxygen.

People often spread myths that we never see blood in its blue form because the instant we get cut, the blood is exposed to oxygen and thus, instantly turns red. Of course, when you get blood drawn from your veins that isn’t exposed to air, we see that it is dark red, but let’s not let such observations get in the way of a good myth.

In reality, it turns out just dark red when blood is deprived of oxygen. You may have come across the fact that while donating blood your blood looks more bright. When it’s oxygenated, it turns a brighter red. This red color primarily comes from the hemoglobin, which contains four heme groups.

These heme group’s interactions with various molecules end up giving it the dark red or light red color. The hemoglobin itself is a protein that binds with oxygen to eventually be distributed throughout the body in blood.

De-oxygenated Blood Turns Dark Red, Not Blue. The basic misguided judgment that blood that needs oxygen diverts blue presumably originates from the way that veins seem blue and blood in the veins is regularly going to the lungs, consequently drained of oxygen