I've just looked at the Begelly website and wonder if anyone who is more knowledeable about monkeys than me can confirm that the patas are different subspecies?
They are about the fattest Patas(it nearly rhymes...) I've seen. I looked in a couple of Monkey books and there's some debate as to whether there are any real subspecies in Patas monkeys. 'Nisnas' which is often used as a subspecific name may not describe a seperate subspecies. The colour of face can vary with region, age and condition apparently.
I can see where you're coming from though as the front one is a plain foxy- ginger colour and the rear one has more peppery grey in the coat.