After death, as normal human blood clots in the veins, it begins to seperate into several different parts, each of which settles out differently. The red cells that give the blood most of its color form into clots that range from dark pink to an almost black shade of red. The other portions form clots that are more white and light gray.
Given the thought that at least some of our zombie cousins are reanimated after a lengthy "at rest" period, the blood in their veins would have more or less solidified, or been replaced by embalming solution. Depending on the method of reanimation: radiation, virus (earth-bound or space-born), industrial accident or heinous experimentation, the zombie blood could take on any number of characteristics, colors and consistencies...
Uhhh, you know what? Just go with a very dark, lumpy green.
Well, you did ask for an expert. My Ph.D. is in "Zombology"
Another excellent project by the way.
Regards,
David G.