Someone took the time to represent race and ethnicity as reported on the 2000 Census data and create a visual representation for the bay area. They also did the same for a bunch of other cities, it is pretty slick stuff that you can see here.
And what do the colors represent? Well, a look at Marin county should tell you what the red dots are for.
Seriously, here’s the breakdown:
Red is White, Blue is Black, Green is Asian, Orange is Hispanic, Gray is Other, and each dot is 25 people.