I'm pretty sure a rock red and a black sexlink are the same thing. Crossing a barred hen with a RIR roo will give you a black sex link. I'm new at this as well but that's what I've gathered from other BYC posts.
I have 4 black sex links and they all look different. One is black with green sheen, one has red highlights on her head and neck and a black body with green sheen, one is black with all over red highlights and the last one looks like shes a golden rir.