What actual dyes are used in filaments?
I spoke with a chemist tonight.   He said to start with the SDS (or MSDS) for the filament,  which is required to be available for most materials.   It should list the pigments and additives if they are not recognized as safe.  If they are safe,  non-toxic, not flammable, non-reactive, they might not be disclosed on the data sheet. 

He warns that sometimes the SDS lists just an industry name for a common pigment,  and sometimes is the full chemical name.   IMO, Google may help with translation. 

The chemist has a deep background in color science and pigments.