I don't know if it's the color choices, the dot placement, or some combination of the two, but this appears misleading to me. Looking at the Central District in Seattle, one could be forgiven for thinking it is a majority black area.[0] In fact, African-Americans only make up ~20% of the population there (very high for the PNW, but hardly a majority). The New York Times census map gives a far more accurate image of the racial demographics of that neighborhood.[1] I believe the NYT map only has one dot per 100 people, which means the dots are larger and less crowded. Notably, the NYT map uses green dots for white population and blue dots for black population - the reverse of the map linked here. That means if the color choices are having an impact on the way we perceive mixed neighborhoods, the effect is the opposite depending on the map you look at (i.e. you are more likely to think a mixed area is majority black when looking at the OP map, majority white when looking at the NYT map). It's worth thinking about color perception and optical illusions when viewing maps like this.[2]
I love map-based visualizations - they're interesting and fun to look at. Nonetheless, I don't think they're the best way of conveying demographic information.
EDIT: Groxx has a fantastic comment about the order in which the dots are drawn. This could explain my observations.
[0] http://imgur.com/SWmuX1b
[1] http://imgur.com/lEwahHd (http://projects.nytimes.com/census/2010/map)
[2] http://www.illusionspoint.com/wp-content/uploads/2010/09/Col...