What's the difference of a "colorant" and a "trace colorant"?

Answer 1

I like the answer above for the first part of your question.

A "trace colorant" would be a much smaller quantity of pigment -- often too small to be noticeable to the naked eye -- mixed in to a large bulk of material to provide some kind of marker that someone could use to trace the source of the pigment in the end product. They might also cause VERY subtle differences in the pigmentation.

"Tracers" or "taggants" enable companies to detect if someone has stolen their formula for a specific product. They also allow law enforcement professionals to determine the source of a material -- forensic science does a lot of that sort of investigation to track down perpetrators of crimes.

Answer 2

A colorant is something added to something else to cause a change in colour. Colourants can be dyes, pigments, inks, paint, or chemicals. For example, this could be adding white to tint a paint, or black to shade a paint, ultimately changing the colour or value.