Bivariate map (weekly blog post #8)

I guess this would actually be considered a trivariate map, but is there anything wrong with a little overachieving and adding an additional stage? This map combines median household income with high school graduation rates and college graduates. The color ramp and individual county values within this map must have been extremely hard to accomplish. Although there are probably a hundred or so distinct colors within this map, the colors don't seem to clash too terribly with one another. I actually think they blend pretty well, but this could be because the three additive colors were chosen to represent the three fields being measured.