Is our blood the color blue before oxygen hits it?
Not really. It is darker than oxygenated blood, but it isn’t really blue. Well, maybe a little blue. Really dark purplish blue.
It is actually pretty hard to see blood without oxygen in it – because blood (really, hemoglobin – the stuff in blood that holds oxygen) is so good at binding to oxygen that you have to keep it in an oxygen free environment if you don’t want it to hook onto some oxygen. Or give it something it likes better – like carbon monoxide. If you’ve ever seen someone with carbon monoxide poisoning, their lips are “cherry red”. This demonstrates that the color of blood is dependent on what is bound to the hemoglobin. Oxygen turns blood the “normal” red, carbon monoxide turns it a brighter red. Carbon dioxide turns it dark purple, or “blue”.
There may be something that will bind to hemoglobin that would turn it bright, cobalt blue, but if here is, I don’t know what it is – and it would probably not be particularly healthy to experiment…..