The suborder Haplorhini was named in...
Dichromatic (two-color) vision, inherited from basal primata, preserved in most members of the platyrhini as well as in all tarsiiformes. Modified to trichromatic (three-color) vision in catarhini and in howler monkeys. This is likely symplesiomorphic with the dichromatic vision in Strepsirrhini (i.e., a trait that both groups share due to common ancestry).
In addition, haplorhines are neotenous compared to other primates. This means that we retain a more juvenile appearance.
Kawamura S., Hiramatsu C., Melin A.D., Schaffner C.M., Aureli F., Fedigan L.M. (2012) Polymorphic Color Vision in Primates: Evolutionary Considerations. In: Hirai H., Imai H., Go Y. (eds) Post-Genome Biology of Primates. Primatology Monographs. Springer, Tokyo