The team think that the animals are rare and are restricted to a part of the forest where they can find the food and habitat they need.
They also have a distinctive “roaring” call, with Amboko saying: “You often hear them, but don’t see them.”
The researchers also believe the monkeys have been hunted in the past, so they hope that now they are classified as a distinct species, the monkeys can be officially protected.
Prof Kate Detwiler, from Florida Atlantic University, believes that their bright facial markings could be a visual signal to other animals, to maybe make them attractive to a mate or for the animals to be able to identify each other.
The researchers say they still have a lot of questions about this newly described, secretive species and want carry out a more detailed survey to estimate their population and study their behaviour.