What actual dyes are used in filaments? I've seen several questions about dyes in regards to food-safety, with no conclusive answers, as well as anecdotes on the RepRap wiki about how the mechanical properties of dyed PLA tend to vary by color. The general unsatisfactory answer is that dyes and additives used are proprietary secrets of filament manufacturers. However, 3D printer filament is a sufficiently large industry, with sufficiently many players now, that many of these "secrets" surely have to be "open secrets" to some extent by now.

What is known about what types of dyes and additives that tend to be used in filaments for 3D printing? Is there information on distinguishing between them with optical, chemical, etc. properties?

My thought is that by knowing some of the common dyes used by some manufacturers, it would be possible to:


choose those if interested in properties of them, and; 
devise test procedures to evaluate if a different/"generic" filament seems to be using the same ones.
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.