Langurs are born with bright orange fur which darkens to black as they age. It's a colour distinction that is thought to make it easier for adults to identify and look after infants.
Senior primate keeper Jane Marshall says Nangua is being raised by what's known as allomothering, in which a group of females participate in raising the infant, passing it around and nurturing it in turns.
"Meili has shown her calmness and experience since the birth, cradling and protecting the baby, but also allowing [other monkeys in the group] Noel and Elke to get close to him," she told the Guardian.
Little Nangua is also doing well: "He's still quite wobbly on his legs, but his head control is very strong and he's gripping and climbing well," Marshall said. "The adults are starting to let him climb off them briefly, which shows they're happy with his progress."
His father, Bobo, who was brought in under a breeding programme from Beijing Zoo in 2010, is said to be protective of his new family.