I've done some research tonight, comparing my photos with pictures in books/on the internet. I've determined this animal more closely resembles the Caquetá titi monkey (Callicebus caquetensis) -my first choice- or Bolivian titi (Callicebus modestus). Any help would be greatly appreciated!
I was doing some research on Callicebus last month, as I had some species to be identified, But I only investigated about Colombian callicebus, Here is a link to the brownish colombian species. Stunning monkey discovered in the Colombian Amazon
I really doubt it is a Callicebus caquetensis, since I dont see any redish part and because It is very unlikely to find a Colombian Endemic in Lima, But you never know, you also saw the Oreonax in Cali so anything can happen
This is a dark morph of the San Martin titi monkey (P. oenanthe). The morph is especially seen in the southern part of its distribution range. There is another picture on zoochat of this animal, together with his hybrid offspring (hybrid with discolor).