For OB, it is much much harder. At a guess I am going to say that one is a male, but I would need more of his dorsal fin. (IE flaring.) If it is rounded it is more likely a female, but if it is a sharp tip likely a male.
(The problem with OB is that because they are hybrid, hence they can get the ob gene, that also means that they take on some of the other appearances.) OF course that means that female have color too.
But the males will still have more color, and likely more of a blue ting to them.
For my first one I found out that it was female because suddenly she was holding...
I
Anyways here here are the only crudy pictures I have:
A male:
A female holding: (She is young though but likely wont show much more color
Sorry but I can't find any better pictures than this at the moment, and of course you can't see the rounded dorsal fin. I will try to add in a picture from some place else.
*/edit/* sorry but I can't find a female picture off of google that I thought showed anything. I only have the 1 female left, and I only have my camera phone for digital photos, but if I get the time I will try to get a snap of her for you so you can compare a little better.)
Also if you want to see more pictures of males check here:
http://www.cichlid-forum.com/profiles/species.php?id=1372