It is true that human blood appears to be blue or deep purple in our veins when it is not exposed to the air. Once the blood is exposed to the air through an opening such as a wound, the oxygen in the air reacts with the blood and give it its bright red color.
Yes and no. Our blood may appear blue or a dark purple but really it's just the different types of veins. If it was true that our blood turns red when it has oxygen in it... Then why when we give blood their is no oxygen in the syringe so why doesn't it come out blue.. Huh? My biology teacher told me this. I hope this helped uou.