Cercopithecus erythrotis at Shanghai Zoo - uploaded on behalf of alexkant

Taken from zooinstitutes.com with the permission of the owner, @alexkant and at his request

Red-eared Monkey - 16/04/2016 | ZooChat

See also here:

@FunkyGibbon Ah, that one is even better

This photo (and the ones by FunkyGibbon) aren't C. erythrotis. They are probably a variant of C. ascanius whitesidei. There is a good side-by-side comparison illustration in Kingdon's Mammals of Afica, where this form is noted as an "unnamed monkey that may be a variant of the Congo Basin Red-tailed Monkey". They look very different to erythrotis.

The photo by @devilfish from Pata Zoo labelled as Red-eared Guenons also shows ascanius.