Another thing to think about is the pigment used is often "carbon black" instead or in addition to some of the other colorful powders that are opaque enough to provide a full pallette, when starting from virgin white or clear polymer pellets. Similar to its use in car tires, carbon black can impart strengthening and durability properties to the final product that other pigments do not exactly match. Now if the final…
Carbon black can also be produced from vegetable matter and is labelled as E153 in the EU for colouring food. It would appear that it's the PAH content of petroleum derived carbon black that is the carcinogenic component https://www.efsa.europa.eu/en/efsajournal/pub/2592
Naively, I would think the paper you linked is about carbon (the charcoaley substance) derived from vegetables being used as a black food coloring, and the poster above is talking about “carbon black oil”, a type of oil derivative that looks black - two completely different things.