Basically, a free person of color (FPOC) was anyone who was not of exclusive European extract during the era of enslavement in this land, who happened to be recognized by the European extracts as 'not enslaved'.
I'm not suggesting that this is the actual definition or the only 'recognized' definition. This is just my understanding of what the term means.
How these people came to be recognized as 'free', I'm sure is as varied as there were FPOC.
Maybe others here have some other definitions.
Eric Thomas