The white circles around their eyes are not actually glasses - the fur there just grows in a different colour. Scientists think it might help them see better in dim forest light, or help them recognise each other in a crowd. Whatever the reason, it makes them look like tiny owls.
Their babies are even more surprising. Dusky leaf monkey babies are born bright orange - almost glowing - which is completely different from their grey parents. The whole troop helps look after the orange baby, and it slowly changes colour over the first few months until it is grey like everyone else.
These monkeys are leaf-eaters - their name says it. Their stomach is divided into chambers like a cow's, which helps them break down tough leaves that other monkeys couldn't digest. They especially love young leaves at the tops of trees, where the sunlight is strongest.
Dusky leaf monkeys live in family troops of around 10-20. They are very calm and gentle, often sitting still for ages watching the forest. The grown-ups quietly groom each other while the children chase up and down nearby branches.