I could be wrong, but it seems like blue veins generally exist closer to the surface of the body rather than arteries. And I'm also wondering if this is evolutionary because during an injury, the outside gets damaged first, and I am just speculating that it's more important for muscle tissue to keep gaining blood than removing already depleted blood, since in the event of an injury, bleeding would cause depleted blood to leak out anyway and the inner blood vessels are less disrupted. Or, if this is simply a trick of the color, that blue veins are just dramatically more noticeable.