I think it would depend if the "normal" clown was a perc or ocellaris. If it were a perc, then you would have some clowns that would have normal perc colorations, some that will end up all onyx, and a combination along the whole spectrum (varying amounts of black in the true perc colors - i.e. NOT a chocolate or mocha clown).
If it were an ocellaris, I'm not as certain how the coloration would develop as this would be a hybrid between species. My guess is something similar to above, but they would develop their bars quicker (as ocellaris tend to do).
Now, if the "onyx" was actually a black and white ocellaris paired with a normal ocellaris, then you would get some variant of the chocolate or mocha clowns. Without proper ID's is a bit of a crap shoot, but these are some of the possibilities what they may turn out to be. (if they are actually spawning of course - I've had plenty of fish do the dance, but not spawn for some time)
