Question: when you bleed and get a blood stain on a fabric why is there a yellow outline around the blood?

Karen answered on 8 Nov 2016:

I assume this is the plasma portion of the blood which is straw yellow in colour (or luminous yellow if you’re jaundiced).
Blood consists of red cells , white cells, platelets and the liquid portion plasma. When you separate blood using a centrifuge you will see 3 layers..,red cells at the bottom, a buffy coat (white cells and platelets) in the middle and the yellow part, plasma on top. Plasma contains proteins such as those involved in blood coagulation (clotting).
Hope this helps☺