During my primates class I was told that in the wild these 2 are very tolerant of each other. The Colobus aren't OK with other families of Colobus monkeys, but they don't seem to have an issue with the Mangabeys being close by. When we had Mangabeys at the LA Zoo, they were housed next door to our B&W Colobus troop, and could see into each other's exhibits. The female Mangabey would frequently sit and watch the antics of our younger Colobus.