Yes, according to Vallejo heavy charcoal is black but It's not...it's a warmer dark grey but definitely not black and regarding German Grey I'd say is a bit colder.
Those charts are offen very misleading, in game color chart comparison it says that opaque heavy red is equivalent to
MC red leather but in fact they are
nothing alike, one is a darker red the other is an orangy brown.
The picture is not perfect and it's not 100% accurate but the difference is very obvious...black vs. heavy charcoal.