Unless you have genetically super high triglycerides, I don’t think your diet will affect the color of your plasma.
I have noticed that premenopausal women have plasma that seems to have a very slightly green tinge, to my eye. Also, at a plasma donation center, where they are drawing your whole blood, adding a bit of anticoagulant, putting it through a centrifuge, drawing off the plasma and returning your red cells to you… you’ll notice that the first draw will be very light and almost straw colored. After several cycles, you’ll notice the plasma getting darker and darker, I believe this is due to some hemolysis that happens when some red blood cells are slightly damaged each cycle and color the plasma accordingly.
The plasma donation center where I go indicates that you should eat a low fat diet the day before your planned donation (and should NOT be fasting) so that the fat in your blood does not slow down the process. One of the phlebotomists showed me a filter with the fat from my blood that is separated out. She said mine wasn’t bad, but if it’s really high it can slow down the draws and returns because it clogs the lines a little and lowers the pressure.
I haven’t ever altered my diet on purpose, and mine is a pretty high fat diet most days.