Nomascus concolor doesn't have white cheeks (males are entirely black). The identification signage at the Philippine zoos seems to be a bit dodgy overall, from what I've seen in photos on Zoochat and elsewhere, so I wouldn't rely on it too much, especially for less common animals.
I think this animal is probably a Northern White-cheeked Gibbon Nomascus leucogenys (as are probably the females in the other photos).
Yea I was worried that this was the case. I hate losing out on possible new species because of faulty zoo signage. Is this confirmed for the photos of the females as well?
Female Nomascus are all quite similar to one another, and also quite variable between individuals as well. Female concolor have dark bellies though (which aren't visible on your photos).
