OK ... I'll ask the n00b question ;)
I can see the difference between chocolates and regular "blackbacks" when plugged into other combos -- and of course, the chocolates have a really neato homozygous "super" form. So, I can see how they are a genuine morph and a neat BP to have around.
I cannot, however, really pick out the difference between a heterozygous chocolate and a "normal" blackback BP. The only trait I can really see (aside from the brown/black back, of course) is that their "alien heads" on the side seem quite distinct. Is there anything else that can be used to pick them out of a crowd (a la the distinct features of yellowbellies, which I still have yet to master), or is it just something where you have to get one from a proven line?
Also, FWIW, I think the chocolates look very different from the sables from the photographs I've seen. The sables seem to have a much busier pattern with a very "granite" look to it, while the chocolates' pattern seems to be much cleaner, with a more distinct black back.
Of course, whether they are somehow genetically related remains to be seen ...