Mysterious indeed. Other than diminishing intensity of hue, I can't imagine the dilution of tomato product with stock doing otherwise. I've no especial expertise in Greek cuisine, but I am living in a town with a strong Greek presence. The preferred sauce is on the sweetish side, not uncommonly cinnamon spiced. Although olive oil is, of course, the dominant fat, it is not at all unusual for local cooks to incorporate butter for greater richness and sweetness; and, yes, a slightly orange tinge. Still, unlikely, a modest pizza establishment employing unnecessary and expensive butter? A quandry.