Separated into two groups based on their coloration, owl monkeys have gray-tan to brown bodies and either gray or red fur on the sides of their necks. They have pale yellow to orange fur on their stomachs, underarms, and inner legs, light gray to white markings above and below their eyes, and three conspicuous, black stripes from the top of their head to either side of each eye and straight down the forehead between the eyes to the bridge of the nose.
Their coats range in thickness and length depending on the altitudes at which they are found, with species living at higher elevations having thicker, shaggier coats than those living at sea level. They are unusual in their appearance compared to other primates because of their disproportionately large, brown eyes which have evolved as an adaptation to their nocturnal lifestyles.The only nocturnal New World Monkey.
Changes in the morphology of the eye and brain of owl monkeys reveal how specialized they have become to keep this nocturnal lifestyle. Though they do see in color, owl monkeys have less acute color vision than other primates. This is not a disadvantage as they are faster at locating and following moving objects at low light levels and have better spatial resolution at low light levels than other primates which helps them capture insects and move through arboreal habitat.