Black-faced Vervet Monkey (Cercopithecus aethiops)
"...black face, white ruff, pale belly, and superbly unapologetic bright blue scrotum"
Description from a (no longer in my possession) wildlife guide to Tanzania
Tanzania - Feb. 2011
Nikon D300S with 500mm f/4 lens, bean bag support
1/250 sec at f/5, ISO 800