Yep! It is false to say non-oxygenated blood is blue. It's still red. All human blood is always red. Your veins look blue because of the varying wavelengths of light and it having to pass through your skin, as well as being absorbed. But our blood, is never blue... ever; that is a wives tale.
So what I have heard in my youth is fake news all along, amongst other urban myths. Ignoranz jeder Art ärgert immer noch! On the bright side, I should be thankful that I am no longer ignorant of this type of urban legen, or widely spread fake news. There were at least two others that I used to believe that turned out to be false. For example, I reluctantly started to believe in the fenine myth that cats always land on their feet, simply because it has been told again and again ad infinitum, but I then eventually found out, in annoyance, that it is fake news. It is the same with what my folks call gallinippers, said to not bite people and kill human-biting pests, bjut the part of it eating other such insects turned out to be fake news.