There are paints and techniques - and probably drugs - that can do that for short periods of time. (Any such drugs are going to eventually run down your health, not lead to longevity.)
True. Those are definite possibilities. However, as evil as the folks are that we are researching, I would not be surprised if the most evil use of blood were not a possibility as well. I hope and wish that that may not be the case. I’d be delighted to be shown that these evil ones are limited to the means you describe. That is my prayer.