I've heard people argue the whole "POC and colored person are the same because they sound similar!" thing, but it completely neglects the fact that whether a term is used derogatorily or not is more important for considering it a slur than just "how it sounds." You'd seldom, if ever, hear people use POC as a slur, but colored person, like you said, has been used as such.

Someone I had relations with said that they don't like p.o.c., the reasoning being that it's a euphemistic way of saying colored person though. For reference they claimed they were ADOS, I can't remember exactly what they preferred me to use while discussing politics. Might've been just black. Idk it was too many bottles of poppers ago. Anyways, I'll use p.o.c. and it's variations here unless someone informs me otherwise I suppose.