I'm not sure I fully understand your question.
UL states that the listing mark on the conduit (LFNC-A or LFNC-B, etc) is the only method approved to identify the type conduit.
The fact that the cover is black does not indicate anything about the listing.
Does that answer your question ?
NEC356.10(6) does not indicate color. LFNC-B NM is available in gray. I have used this type of tubing for direct burial (for well systems line protection) 60deg wet distribution. I have not run across black LFNC-B as of yet. rbj