Why Blood is not Blue:
If you look closely at the inside of your wrist, you’ll probably see a small network of blue veins running up into your hand. Despite what they might teach you in elementary school, that’s not blue blood running through there. The myth is that deoxygenated blood is blue, while blood leaving the heart is red because it’s been filled with fresh oxygen. When you bleed, the blood is immediately red because it’s exposed to oxygen in the air.
But if you’ve ever given blood or had blood taken at the doctor’s office, you’ll know that it’s not some alien blue liquid filling up that sealed tube—it’s, well, it’s blood. The reason your veins look blue is a simple trick of the light, and the way your eyes percieve colors. When light filters through the layers of skin, the low frequency wavelengths (like red) are refracted by pigmentation and thin fat layers, leaving mostly blue light to reflect back to your eyes. An albino person will usually have red veins because of the lack of pigmentation in their skin.