The color of blood without oxygen is dark red and not blue in color.
Although blood without oxygen may appear as blue in color through the skin as a result of how light interacts with the tissue, the actual color of the de-oxygenated blood is a deep red color.
The de-oxygenated bloods color is also often described as a maroon or burgundy color, according to some science resources.
It's a misconception that the de-oxygenated blood is blue as it appears that way from the way the skin and veins reflect light.
Human blood is never blue in color.
The bluish color of the human veins is only an optical illusion.
Blue light does not penetrate as far into tissue as red light.
And if the blood vessel is sufficiently deep, your eyes see more blue than red reflected light due to the blood's partial absorption of red wavelength.
Medical images also often portray blood in veins as blue to differentiate de-oxygenated blood (blood with low oxygen levels) in veins from the oxygenated (oxygen-rich) blood in arteries.
Healthy blood is typically red in color, although the shade can vary.
Oxygen-rich blood, like the blood found in arteries, is a bright, cherry red.
Blood returning to the heart via the veins, which has less oxygen, is a darker, purplish-red.