The green colour in Orks is caused by the process of photosynthesis in the chloroplasts.
You must realise, however, that photosythesis in plants and fungi produces chemical energy for the cell itself, not the other cells. Ergo, Orks must eat like any other animal, in order for the non-fungi cells to live.
Yes, I know that I didn't answer the question, but providing facts is allowed, I think...
Also, Ork blood will be red, as the animal cells will need pure oxygen, provided by Iron coated red blood cells.
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