I would try white sand with a generous sprinkling of black gravel at the top. All those fish would rather root in sand than gravel...so for rooting fish, I always use regular white/beige sand. Here's an article about sand from Cichlid Forum:
http://www.cichlid-forum.com/articles/sand.php
If you definitely for sure don't want sand, I think your black gravel will be ok. Personally I just don't like the black background and black substrate look...it's done so often, I'm sort of sick of seeing it. I know I'm in the minority here
Don't get me wrong, it looks great in a heavily planted tank. But in a cichlid tank where you're going to have no live plants (probably) then sand with a sprinkling of gravel looks better in my opinion. This is kind of what I mean:
http://img.youtube.com/vi/7JjRLqTxGQs/0.jpg