The blood inside your veins is blue
Veins under pale skin often look distinctly blue, and the claim that blood only turns red once it hits the air gets repeated often enough to sound settled. Is the blood actually blue in there?
Myth or fact? Reveal
Myth. It's a myth. Deoxygenated blood is dark red, never blue, human blood isn't blue at any point in the body. Veins look blue because of how skin and tissue scatter and absorb light before it reaches your eye, not because of the blood's real color.
— Live Science, Blood in Your Veins Is Not Blue, Here's Why It's Always Red