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 product is always going to be black anyway, then you wouldn't really need to start with clean virgin plastic, you could actually use some pretty ugly stuff and cover up unsightliness or inconsistency better in black.
Well the carbon black is made from a "special" oil scientifically known as CBO. I know the chemical jargon can be confusing most of the time so just take my word for it that the "full chemical name" is Carbon Black Oil. Unintuitive nomenclature, but aren't they all ;)
CBO is from some real dregs of petroleum refining, it is raw material that is going to be coked further and it does not need to pass the kind of testing that is required for black fuel oils. Shady operators have targeted these heavy black oil stocks as diluents for their non-refinery chemical byproducts that would otherwise end up as "chemical waste" in some cases.
In the heavy oil lab where people are checking things like viscosity or flash point, you need good ventilation all the time everywhere and never turn off the hoods. It has to be below acceptable levels without a respirator when an H2S-bearing crude is being handled. You still smell it because H2S is just that rough, but at least it doesn't linger and it's not enough to give you a headache. Tolerable now, not like it was decades ago before they started certifying fume hoods.
CBO doesn't have any H2S but it is never tolerable. It bears quite a variety of disagreeable notes that do not resemble any characteristic form of crude or refined petroleum, and it is often described as "weird smelling" by experienced oil chemists. The variety is amazing and hard not to notice, some batches are just so different and others so repulsive. This is when the most sensitive people reach for their respirators, even though they are just fine handling pure benzene without, because the ventilation really is that good.
Bon appetit !