The used veg oil from Thai restaurants is quite dark in colour. Probably from the colour of the spices they use in the cooking. Even after several months of settling the colour remains. I imagine it would remain even if the oil was reacted to make bio. I filter to 5 micron and then leave the filtered oil in plastic containers for months again and although the dark colour remains I do get a fine powder? settling in the bottom of the containers. seems to be less than 1 micron so I am assuming it is not harmful but who knows? I wonder if powder washing would remove the spices (if that's what it is) and lighten the colour.