I'm pretty sure blood is a blueish/purple color until it is oxygenated (spelling?). So the blood inside your body is only red after it passes through your lungs and absorbs oxygen. Like Mytch said, I don't think your blood is ever going to be as blue as the sky, as some may be thinking. But the purplish/blue color is before the blood is oxygenated by the lungs. At least, this is what I remember being true.