The baboons to the west of Mt Kenya are pure-bred olive baboons, therefore, these are olive baboons. The populations to the east and south of the Mt Kenya area readily hybridise with yellow baboons to the extent that it can be impossible to say which species some animals belong to. There are seven sub-species, mainly due to hybridisation with other species, to my knowledge the ones at Lake Nakuru are the nominate P.a.anubis race. In fact it was itself considered a sub-species of the hamadryas baboon (Papio hamadryas), only becoming accepted as a species in its own right 15 or so years ago.

Another good example for the discussion of speciation at:

http://www.ispot.org.uk/node/10934

Unlike the smooth haired yellow baboons you most often see in zoos, this species has shaggy, 'blow-dried' look.

Ta for that - as with the colobus info, very interesting and not an area I know a lot about.