I have been donating blood to the Red Cross since 1970 or almost 42 years. It is more than a habbit; it is a calling! Recently, I have done the "double red blood cell" transfuson. This means the blood is taken from my arm, run through a centrafuge to seperate out the red blood cells and the plasma is returned to me. The dark colored fluid is the blood leaving and the straw colored fluid is the plasma returning.
Actually, if you are not tracking the change in color and realize it is the change in the nature and direction of fluid flow, you would think it simply a plastic tube with two different colors of core (within the tube). Now you know, one is bleeding out (red) the other is "bleeding back" (straw).
You should try it. It is needed and is worth doing. At a Lions District meeting luncheon, I told one person (an RN) about this double red blood cell donation. I said "it is more pleasant than regular donations". Another person listening to me agreed with "it is more pleasant". This RN sniffed at both of us and said "you're twisted!"
The next time I saw her, I said "I'm still twisted". I got another nasty look...
The straw colored fluid is plasma being returned to my body. The abrupt change to red as the switch from returning plasma to sucking out blood!