So how do you make oil and water mix? You need an emulsifier. To get past racism, you need common ground that people agree on -- or you need something that attracts people who prefer diversity to division. For instance, you could offer tax breaks based on diversity: the more diverse the organization, the bigger the break, based on composition of employees or better yet board members. You could launch a college offering free education based not on test scores but student participation in diversity (e.g. foreign languages, international travel, working a social justice job). The same approach would apply to a housing complex; there are places in Europe offering discounted housing for people who want to mingle with immigrants, and it works.
People remain separate because a majority prefer it that way. They're not going to fix this, because they don't want it fixed. And if they have to be seen "doing something," they'll make sure it won't really work.